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HANDBOOK

INVERTEBRATE ZOOLOGY.

C? 7?

HANDBOOK

INVERTEBRATE ZOOLOGY.

FOR

LABORATORIES AND SEASIDE WORK.

W. K. BROOKS, PH.D.,

ASSOCIATE IN BIOLOGT AND DIRECTOR OF THE CHESAPEAKE ZOOLOGICAL LABORATORY

OF THE JOHNS HOPKINS UNIVERSITY.

BOSTON:
S. E. CASSINO, PUBLISHER.

1882.

BOSTON STEREOTYPE FOUNDRY, PRESS OF STANLEY & USUEK,

No. 4 PEARL STBKKT. 299 WASHINGTON STKEET.

INTRODUCTION.

fFIIIS book is a handbook, not a text-book, and the
entire absence of generalization and comparison is
not due to indifference to the generalizations of modern
philosophical morphology, but rather to a wish to aid
beginners to study them.

Most lecturers upon natural science find, no doubt,
that preliminary work, the presentation of the facts upon
which science is based, absorbs so much time that there
is no room for a philosophical discussion of the scien-
tific aspects of the subject.

I have, therefore, attempted to show the student how
to acquire a knowledge of the facts for himself, in order
to remove this burden from lecturers and text-books.

The types selected for description are necessarily few ;
but I hope that a thorough study of all the forms which
are here described will fit the student for more exten-
sive research.

In the treatment of each type I have not attempted
to make an exhaustive monograph for the use of special-
ists, or to present all that is known about it ; but sim-
ply to call the attention of the beginner to the struc-
tural features which he can readily observe for himself.

VI INTRODUCTION.

There are many facts of the greatest importance, which
the beginner must accept on authority, and as reference
to facts of this sort, in an elementary description, for use
in the laboratory, could hardly fail to create confusion,
such references have been omitted.

The concrete description of specific forms demands
figures of the species described, and as it is important
that these figures should show nothing that the beginner
cannot himself discover in his specimen, the complicated
figures which accompany most monographs were found to
be impracticable, and most of the cuts have been made for
the purpose, by photographic reproduction of the author's
drawings, or of drawings made from nature under his
direction.

Where it has been thought best to reproduce a figure
from a monograph, the author has drawn it with a pen,
and this drawing has been photo-electrotyped.

It is hoped that the practicability and significance of
the cuts, as guides to dissection and study, will more than
compensate for the artistic finish and technical skill which
has been lost by the employment of this method of
reproduction.

CONTENTS.

SECTION PAG«

I. THE STRUCTURE OF AAKEBA 1

II. THE STRUCTURE OF PARAMCECIUM 7

III. THE STRUCTURE OF VORTICELLA 12

IV. THE MULTIPLICATION OF VORTICELLA . . . .19
V. CALCAREOUS SPONGE 22

VI. THE STRUCTURE AND GROWTH OF THE ASEXUAL FORM

OF A CAMPANULARIAN HYDROID 30

VII. THE STRUCTURE OF AN OCELLATE HYDRO-MEDUSA . 37

VIII. THE MEDUSA STAGE OF A CAMPANULARIAN HYDROID, 49

IX. THE STRUCTURE OF A STARFISH : THE HARD PARTS . 56

X. THE STRUCTURE OF A STARFISH: INTERNAL ANATOMY, 63

XL THE MICROSCOPIC STRUCTURE OF THE STARFISH . . 73

XII. THE HARD PARTS OF A SEA-URCHIN .... 83

XIII. THE INTERNAL STRUCTURE OF A SEA-URCHIN . . 91

XIV. THE EMBRYOLOGY AND METAMORPHOSIS OF ECHINO-

DERMS 99

XV. THE GENERAL ANATOMY OF THE EARTHWORM . . 140

XVI. THE MICROSCOPIC STRUCTURE OF THE EARTHWORM . 152

XVII. THE GENERAL ANATOMY OF THE LEECH . . .160

XVIII. THE HARD PARTS OF THE COMMON CRAB . . .168

XIX. THE HARD PARTS OF THE CRAYFISH OR LOBSTER . 185

XX. THE GENERAL ANATOMY OF A CRAB . . . .190

XXI. THE METAMORPHOSIS OF A CRAB . 207

31202

VJ11 CONTENTS.

XXII. THE ANATOMY AND METAMORPHOSIS OF CYCLOPS . 223

XXIII. THE HARD PAJRTS OF A GRASSHOPPER . . . 237

XXIV. THE INTERNAL ANATOMY OF A GRASSHOPPER . . 258
XXV. THE GENERAL ANATOMY OF ANODONTA . . . 269

XXVI. EXAMINATION OF TRANSVERSE SECTIONS OF UNIO OR

ANODONTA 285

XXVII. THE LAMELLIBRANCHIATE GILL 296

XXVIII. THE DEVELOPMENT OF LAMELLIBRANCHS . . .311

XXIX. THE GENERAL ANATOMY OF THE SQUID . . . 332

XXX. THE DEVELOPMENT OF THE SQUID .... 364

HANDBOOK

INVERTEBRATE ZOOLOGY.

I. THE STRUCTURE OF AMCEBA.

(Amoeba proteus.)

AMCEB^E are frequently to be found in abundance in
the superficial ooze which forms a thin layer upon the bot-
tom of nearly every quiet body of fresh water. The ooze
may be collected from a pond, stream, or ditch, by gently
and slowly skimming the bottom with a tin dipper fastened
to a long handle. In gathering the ooze be careful to
barely skim the surface, and to avoid disturbing the black
mud which usually occurs just below the ooze.

Transfer the material thus gathered to a collecting-
bottle, and gather ooze from several bodies of water, pre-
serving each specimen in a separate bottle, for amcebee
may be abundant in one locality and almost absent in
another.

Pour the ooze into shallow dishes, such as soup-plates
or baking-dishes, putting enough into each dish to form a
layer about an eighth of an inch deep over the bottom.

Place the dishes near a window, where they will be
well lighted without exposure to the direct rays of the

2 HANDBOOK OF INVERTEBRATE ZOOLOGY.

sun; fill them with fresh water, and allow them to stand
undisturbed for two or three days, in order to allow the
amoebae to creep out of the ooze and accumulate at its
surface.

If a permanent supply of amcebre is desired, each dish
may be converted into a small aquarium by the addition
of a few floating water-plants, such as "duck-weed," and
v, hen covered with a pane of glass, to exclude dust and
prevent excessive evaporation, may be kept in good order
for several months by simply replacing with fresh water
the loss by evaporation.

In a day or two a thin brownish-yellow film will usually
be visible over the whole or parts of the surface of the
ooze ; and portions of this film, almost entirely made up
of microscopic organisms which have crept to the sur-
face, may now be examined for amu-ba1, in the following
manner : —

Compress between the fingers the upper bulb of a
medicine-dropper, — a glass tube drawn out to a point at
one end, and furnished with a rubber air-chamber at the
other, — and then pass the pointed end of the tube into
the water close to the surface of the yellow film, and re-
lax the pressure on the bulb. The water will rush into
the tube and carry a little of the film with it.

Take the tube out of the water ; hold the tip over the
centre of a clean glass slide, and, gently compressing the
bulb, force a drop or two of the water out of the tube on
to the slide.

Cut a strip of writing-paper about a quarter of an inch
wide, and, moistening one end of it with water, cut off
about a quarter of an inch from the moistened end and
lay it upon the slide close to, but not so as to touch,
the drop.

AMtEBA.

Carefully wipe a thin glass cover, breathe upon it, and,
resting one edge of it upon the side of the drop opposite
the piece of paper, gently lower the cover on to the paper,

FIG. 1. Amoeba proteus, magnified two hundred diameters.

a. Endosarc. b. Simple Pseudopodia. c. Ectosarc. d. First stage
in the growth of a Pseudopodium. e. Pseudopodium a little older than d.
f. Branched Pseudopodium. y. Food vacuole. h. Food ball. L Endo-
plast. k. Contractile vesiole.

thus spreading out the drop into a very thin layer. A
needle fastened into a handle should be used to lower the
cover into place.

HANDBOOK OF INVERTEBRATE ZOOLOGY.

Place the slide upon the stage of the microscope, and
examine it with a magnifying power of two hundred or
three hundred diameters. If careful examination leads to
the discovery of no amu-ba1, examine the oo/e from another
locality in the same way. It is extremely difficult to tell
a beginner exactly what to search for. If the student is
working under guidance, the instructor should find an
amoeba, and after the student has had an opportunity to
see it he may hunt for others. If Avorking alone, the
student should read the following description, 'and then
hunt for an object which agrees with it.

Having found an amoeba, note : —

I. The irregular, granular, nearly colorless body, which
is made up of an ill-defined central portion (Fig. 1, a), and
a variable number of irregular processes, the pseudopodia
(Fig. 1, b). The body may be nearly spherical and the
pseudopodia small, or the body may be almost absent and
the pseudopodia large, and the animal may pass through
all the intermediate stages between these tAvo forms in a
feAV minutes, or it may remain without change for several
minutes, especially if it has just been transferred to the
slide. The very much branched forms, like the one
figured, are most common in a drop which has been for
some time on the slide undisturbed.

II. The body consists of a pale, nearly colorless, jelly-
like substance, the sarcode, in which tAvo layers AA'ill be
recognized.

a. The outer layer or ectosarc (Fig. 1, c) forms a trans-
parent, very slightly granular film over the entire surface.

b. The darker, more granular eit< Injure fills the interior
of the body and extends into the pseudopodia. It con-
tains many bodies, which will be noticed later. There is
no abrupt line betAveen the ectosarc and endosarc.

AMOEBA.

III. Make a series of sketches of the outline at as short
intervals as possible, to show the changes of form.

IV. Study the growth of a pseudopodium. At first it
is a simple transparent protrusion (Fig. 1, d) of the
ectosarc, looking like a drop of fluid which has been
squeezed out of the body. As it increases in size, the
granular endosarc suddenly rushes into it (Fig. 1, e). It
may then elongate until it forms a long, blunt, finger-like
process, which may remain simple for some time (Fig. 1,6),
or it may branch (Fig. I,/), by forming new pseudopo-
dia along its sides. Notice that, as the pseudopodium
grows, the endosarc flows into it with a well-marked cur-
rent. In this way the whole body may flow forward
into an advancing pseudopodium, which is thus converted
into the body of the organism, and may throw out new
pseudopodia in the same or in a different direction. Note
that, while progressing in this manner, the organism is
specialized into : —

a. An anterior progressing region, with numerous grow-
ing pseudopodia, and, —

b. A posterior or " following" region, with few pseudo-
podia. This posterior region frequently has a well-marked,
rounded outline covered with small eminences, the last
traces of the vanishing pseudopodia. Note that many of
the pseudopodia disappear or are withdrawn into the body
or into other pseudopodia almost immediately after they
become visible.

V. Foreign bodies contained in the endosarc : -
a. The food vacuoles. The endosarc of most speci-
mens will be found to contain small, nearly spherical pel-
lets of food, usually of a yellowish-brown color, although
the color varies according to the character of the food.
In most cases a clear, transparent space surrounds the

6 HANDBOOK OF INVERTEBRATE ZOOLOGY.

food ball, and is filled with water which has been swal-
lowed with the food. The ball of food, with its .surround-
ing water, is a food vacuole (Fig. 1, g). After a time
the water disappears, and a number of food balls, without
the layer of water, are usually present (Fig. 1, //) . Some-
times the endosarc contains drops of water without food
matter.

b. Occasionally the endosarc contains the entire bodies
of small organisms, such as rotifera, alga,', etc., which have
been swallowed as food.

c. Occasionally the endosarc contains other foreign
bodies, such as grains of sand, particles of sawdust, etc.

d. If possible, watch the process of ingest ion of food
matter, the formation of a food vacuole, and the expulsion
of indigestible matter from the body. Notice that food
may pass in or be expelled at any point on the surface.

VI. Structural constituents of the endosarc : —

a. In some specimens the endosarc will be found to
contain a discoidal or spherical transparent body, the endo-
plast or nucleus (Fig. 1, i). It does not change its form
with the movements of the body, and it usually lies near
the posterior end when the organism is progressing. It
may be surrounded by an area of non-granular endosarc.

b. In some specimens a clear, transparent, liquid globule,
the contractile vesicle (Fig. 1, A-), may be found, usually
behind the nucleus. If carefully watched, it will be seen
to gradually enlarge for several seconds and then suddenly
collapse and disappear, to reappear again in a few seconds
at the same or nearly the same place.

c. The endosarc usually contains other bodies, such as
crystals, large granules, and drops of oil.

VII. Make sketches showing as many of these points
as possible.

PARAMCECIUM.

II. THE STRUCTURE OF PARAMCECIUM.

(Paramoecium caudatum.)

SPECIMENS of the holotrichous infusoria will usually be
found in the material which has been collected to obtain
amceboe, and an abundant supply may be procured in the fol-
lowino- manner : Fill a small glass beaker or tumbler with

O O

water from one of the amoaba-aquaria described in the last
section. Place a small handful of pieces of hay or dead
moss in the water, and allow it to stand in a warm place
for about a week. In the winter it may be placed in the
direct sunlight, and even in summer the sunlight will not
usually be injurious. After a few days a white film will
appear upon the surface of tho water ; and if the lower
edge of this film be carefully examined where it touches
the glass, great numbers of rapidly-moving white animals,
so small as to be barely visible without a lens, will
usually be found. When examined with the microscope
many or most of these organisms will be found in nearly
every case to belong to the species which is here described,
but even if this species is not found, almost all the points
of the description may be verified in any of the holotrichous
infusoria.

Transfer a drop from the surface of the water to a glass
slide by means of a dropping-tube, in the way which has
been described in Section I. Cover it with a thin glass
supported by a small piece of paper or a hair, and examine
it with a magnifying power of eighty or one hundred
diameters, and notice the oval animals gliding actively
across the field of view. Find one whose motions are
somewhat restricted by the cover, and, after placing it as

HANDBOOK OF INVKK TEMKATE ZOOLOGY.

..- b.

nearly as possible in the centre of the field, remove the
objective from the microscope and replace it by one mag-
nifying two or three hundred diameters.

FIG. 2. ParamcKcium caudatum. From H.
J. Clark, Mind in Nature, Fig. 90. Side vir\v ;
magnified about three hundred diameters.

a. Anterior end. b. Contractile vesicle
during a period of contraction, c. Con-
trurtile vesicle during a period of dilation.
d. The vestibule, e. The oesophagus. /.
The anus. g. Food vacuoles. It. Nucleus.
i. Food balls, k. Long cilia at the posterior
end of body. I. Ectosarc. in. Endosarc.

Having found the animal again,
notice : —

I. The soft, flexible, transparent
body (Fig. 2), oval when viewed
from above and below, and some-
what slipper-shaped in side view.
The posterior end (Fig. 2, A') is
bluntly pointed, and forms the to I'
of the slipper, while the anterior
end (Fig. 2, «) is rounded and
somewhat twisted, so that the out-
line of one side of the anterior end
is bent into a shape somewhat
like the figure 8. As this side is
quite generally uppermost it may
be called dorsal.

II. The entire surface of the
body is covered with fine hairs or cilia, which are in con-
stant vibratory motion. Along the edges of the body
they can be seen without difficulty, but upon the surface
they are visible only as fine dots. The cilia are of two
kinds.

PARAMCECIUM. 9

a. The locomctor cilia, which are quite small, and cover
nearly the whole of the body. By their vibration the
animal is made to move through the water. At the pos-
terior end of the body there is a small tuft of much larger
cilia (Fig. 2, A).

b. Around the edges of the 8-shaped outline of the
anterior end, notice a row of much larger cilia. These
give rise to currents by which floating particles of food
are carried into the mouth, which is situated on the pos-
terior bend of the 8 .

III. The surface of the body is covered by a thin, deli-
cate, transparent cuticle, which is rather difficult to see
satisfactorily. The cilia are protruded through holes in
the cuticle, and if one of the animals be placed upon a
slide in a small uncovered drop of water, and watched as
the water evaporates, a good view of the cuticle and its
perforations may usually be obtained just at the time
when the animal begins to dry.

IV. The body-substance or sarcode. The transparent,
somewhat granular, body-substance fills the entire space
inside the cuticle, and is pretty definitely divided into two
layers, which are much more distinct and sharply separated
than they are in amoeba.

a. The transparent outer layer or ectosarc (Fig. 2, if),
which lines the cuticle.

I. The much more fluid endosarc (Fig. 2, m), which
fills the space inside the ectosarc, and is much more
granular. It usually contains oil-globules, colored par-
ticles, and various foreign bodies which are not found in
the ectosarc.

V. Watch a paramcecium push its body into a narrow
space between the particles of sediment in the water.
Notice that the more fluid endosarc is pushed back by the

10 HANDBOOK OF INVERTEBRATE ZOOLOGY.

obstruction and accumulates at the posterior end of the
body while the ectosarc still follows the outline of the
cuticle. After part of the body has been pushed past
the obstruction, the endosarc, with the particles which it
contains, flows rapidly through the narrow part into the
enlargement beyond.

VI. Watch one of the larger particles in the endosarc
for some time, and notice that it has a motion which is
independent of the changes in the shape of the body. It
will be found by very careful examination that the endo-
sarc, with all its contained particles, is slowly circulating
around the body, up one side, and down the other, as
shown by the arrows in the figure.

VII. The digestive organs. These can be most satis-
factorily studied after the animal has been fed with some
colored substance, such as powdered carmine or indigo.
Place a drop of water, with paramu-cia. upon a slide, and
mix with the water a little finely-powdered indigo ; cover
the specimen gently with a cover-glass, and examine with
a magnifying power of about two hundred diameters,
noticing : —

a. The currents which are caused by the small locomo-
tive cilia.

b. The peristome or 8-shaped line of large cilia at the
anterior end of the body, by the action of which the car-
mine is swept into, —

c. The vestibule, a widely-open, funnel-shaped chamber
(Fig. 2, d) lined with cilia, and situated in the posterior
bend of the 8.

d. The oesophagus, a ciliated tube which runs down-
wards and backwards (Fig. 2, e) into the .substance of the
endosarc. In this tube the particles of indigo are grad-
ually rolled into a pellet, and from time to time these pel-

PAKAMCECIUM. 11

lets are forced, by the contractions of the body, out of the
inner end of the tube into the endosarc.

e. One of the pellets, together with a little water swal-
lowed with it, forms a food vacuole, of which several (Fig.
2, g) may usually be seen in different parts of the body.
A food vacuole is a spherical space filled with water, and
containing solid particles of various kinds. As the vacu-
oles are carried around the body by the circulation of the
endosarc, the water and soluble parts are digested out,
until at last only the indigestible parts remain embedded
in the sarcode as a food ball (Fig. 2, z).

f. The anus. After a time these particles accumulate at
a point (Fig. 2,/1) upon the dorsal surface about halfway
between the vestibule and the posterior end of the body.
The ectosarc becomes thin over them, and they are then
driven out of the body through a temporary anus, the
location of which is permanent.

VIII. The contractile vesicle. If a specimen which is
pretty quiet be carefully watched, a large transparent
space will be seen at some point in the body, and after
remaining visible for some twenty or thirty seconds, it
will suddenly disappear and gradually reappear. In some
species there is one near each end of the body (Fig. 2,
b and c), and in others only one, near the middle. When
they first appear they are very small ; they gradually in-
crease in size until they are quite conspicuous, as shown
at c in Fig. 2. Uadiating channels then make their ap-
pearance and extend from the vesicle into the surround-
ing endosarc. The vesicle now suddenly contracts and
disappears, its contents being forced into the tubes, which
are visible for a short time longer, as at b in Fig. 2, and
then gradually disappear also. In a few seconds the vesi-
cle reappears at the same place.

12 HANDBOOK OF INVERTEBRATE ZOOLOGY.

IX. The nucleus and nucleolus. In some species there
is one nucleus or endoplast at each end of the body, and in
others only one near the middle. They are club-shaped
musses (Fig. 2, //) of granular protoplasm of a firmer con-
sistency than the surrounding endosarc. They are some-
what difficult to .see in the living animal, but they may be
made more conspicuous by adding a little acetic acid to
the water. Close to the nucleus is a much smaller body,
the nucleolus.

X. Make a sketch showing as many of these points as
possible.

III. THE STRUCTURE OF VORTICELLA.

ANY of the numerous species of Peritrichous Infusoria
may be used to verify the following description, since the
differences between them are very slight. The Vorticel-
lidae are abundant in both fresh and salt water; and many
specimens will probably be found in the hay i illusion,
which has been employed to propagate Paramcecia.
Good specimens for examination may nearly always be
obtained from a small aquarium, which has been well
stocked with water-plants and kept for a few weeks in a
well-lighted place. A glass gallon-jar makes a very con-
venient aquarium for this purpose, and it should contain
no fishes, newis, or other animals large enough to devour
the vorticellas.

Although the individuals are microscopic, they are
frequently found, in such an aquarium, in colonies of
a sufficient size to be recognized by the eye without
difficulty.

If the leaves and stems of the water-plants are care-
fully examined, under water, either with or without a

VORTICELLA. 13

hand-lens, some of them may be found to carry minute
white flocculent spots or tufts which resemble spots of
mould. If one of these tufts be gently touched with a nee-
dle or a hair, it will instantly shrink back, until it is re-
duced to an almost invisible white spot. After the
disturbance ceases, it soon expands again to its former
size.

Having found one of these tufts, grasp with a pair of
forceps the leaf or stem which carries it, and cutting out the
piece with a pair of scissors, transfer it to a drop of water
upon a glass slide ; cover it with a cover-glass, which may
be supported by a piece of paper, if necessary, and exam-
ine it with a magnifying power of about eighty diameters.

AVhen thus examined, the wrhite tuft will probably
prove to be a colony of Vorticellidae, but it may, per-
haps, prove to be a colony of Stentors or even of Roti-
fera. If the student finds that he is unable to verify the
following description, he should ask his instructor to ex-
amine his specimen.

Having found a colony of Vorticellidse, notice : —

I. The bell-shaped bodies of the individuals which
compose the colony.

II. The stem which projects from the
small end of the body of each animal, and
joins it to the others and to the supporting
body (see Fig. 3).

FIG. 3. — Diagram of a colony of Vorticellae, magni-
fied about fifteen diameters. FIG. 3.

III. The cilia around the margin of the bell.

IV. Keeping the eye at the microscope, tap the slide
gently, or touch the animals with a hair, and notice their
rapid contraction.

a. The edge of the bell bends inwards so that the body
becomes nearly spherical.

HANDBOOK OF IN VKKTHKUATE ZOOLOGY.

b. The stem is thrown into a spi nil, thus dragging the
body back towards the point of attachment.

c. Watch the changes by which the colony gradually
expands after the disturbance ceases.

1. The steins straighten.

2. The rims of the bells arc slowly everted.

3. The cilia suddenly resume their active motion.

d. Notice the marked contrast between the rapid con-
traction and the gradual expansion.

V. Make a sketch of the community, showing as many
of these points as possible.

VI. Study a portion of the community with a magnify-
ing power of 200 to 500 diameters, and notice : —

a. The body of a single animal : circular when seen
from above or below, and bell-shaped in side view, and
attached to a stem by its lower or narrow end.

1. The upper edge of the bell is bent out to form a

thickened marginal rirn,
the peristome, Fig. 4, c.

2. Notice the crown of
large cilia carried by the
peristome.

FIG. 4. — A single adult, fully
expanded individual of Vorti-
cella nebulifera (Ehrb. ) magni-
fied about six hundred diameters.
(>>'//;/ ////// altered from Ertrt*.
Untersuchunf/en an Vorticella
Nebulifera, von Dr. jilril. E<ln«i-d

Everts; Zeitf. Wiss. ZooL xxiii. 592: 1873. Taf.

xxx. fig. 1).

a. Cilia of ciliated disc. 6. Ciliated disc.

c. Peristome. d. Vestibule. e. (Esophagus.

/. Contractile vesicle, g. Food vacuoles. /;. En-

doplast. i. Endosarc. k. Ectosarc. I. Cuticle.

in. Axis of stem.

Pro. 4.

VORTICELLA. 15

3. The mouth of the bell is nearly filled by a struc-
ture (Fig. 4, b), which may be compared to the clapper
of a bell, and which is known as the ciliated disc or e/>/x-
tome. Its outer or upper surface is slightly arched ; and
there is a second circlet of long cilia (Fig. 4, a) around
its edge.

4. Around the greater part of its circumference the cil-
iated disc is united to the peristome ; but on one side there
is an open space, the vestibule (Fig. 4, d), which is
bounded internally by the disc, and externally by the
peristome.

5. Notice that, when the animal is fully expanded, the
plane of the peristome makes an acute angle with the
plane of the ciliated disc : the vertex being opposite the
vestibule.

6. In the lower part of the bell notice a number of faint
longitudinal striations which may, in favorable specimens,
be seen to cover the whole surface of the bell up to
the peristome.

b. The stem is cylindrical, and consists of an outer,
transparent sheath (Fig. 4, I) and a central, darker axis
(Fig. 4, wi), which is not straight, but arranged in a
loose spiral inside the tube formed by the outer sheath.

c. Make a sketch showing these points.

VII. Selecting an individual with a short stem, watch
the process of contraction, and notice the following
changes : —

a. The ciliated disc is first withdrawn into the bell by
a process of rotation upon the peristome at a point oppo-
site the vestibule.

b. The cilia of the peristome cease vibrating and fold
in over the disc.

c. The peristome next folds inwards and contracts, and
the body becomes nearly spherical.

16 HANDBOOK OF INVERTEBRATE ZOOLOGY.

d. The stem is thrown into a spiral.

VIII. Notice that this order is reversed during expan-
sion, which takes place much more slowly.

IX. The Structure of the Body.

As in Paramcrciimi, the body-substance consists of
three layers, — the cuticle, the ectosarc, and the endosarc.
a. The endosarc (Fig. 4, z, Fig. 5, d) occupies the
central region of the body, but does not extend into the
stem. Its transparent, colorless sarcode contains numer-
ous minute, dark-colored granules, and it also contains
food vacuoles (Fig. 4, #), oil-drops, and foreign border
such as have been noticed in Paramo3cium and Amoeba.

1. Careful observation of a single vacuole or solid par-
ticle will show that the whole semi-fluid endosarc is in mo-
tion. The motion is most vigorous near the surface, and
least so in the centre. If the animal be placed with the
ciliated disc above, and the vestibule away from the ob-
server, the current will be found to flow
down the left side, across the bottom, and
up on the right side, as shown in Fig. 5,
by the arrows.

FIG. 5. — Diagram of a vertical section of Vorti-
cella nebulifera, to show the arrangement of the
layers of the body (from Everts).

a. Cuticle, b. Contractile layer of Ectosarc.
c. Inner layer of Ectosarc. d. Endosarc. e. Endo-

.r IG. 0. _ . „

plast. /. Stem.

2. Notice the movements of the semi-fluid endosarc
caused by changes in the shape of the body, and carefully
distinguish these movements from the constant circulation
of the endosarc.

b. The ectosarc (Fig. 4, k and Fig. 5, c) is thin above ;
but it gradually thickens below, and it forms the entire
axis of the stem. The line separating it from the endo-

VORTICELLA. 17

sarc is more definite than it is in Amoeba or Paramoecium.
The ectosarc is uniformly granular, and it contains no food
vacuoles, oil-drops, or foreign bodies.

3. The ectosarc, like the endosarc, is in constant motion ;
but, oAving to the absence of large particles, the currents
:irc very hard to discover. They flow in an opposite di-
rection to those of the endosarc.

4. The longitudinal striations are restricted to the
outer surface of the ectosarc, which is thus divided into a
superficial muscular or contractile layer (Fig. 5, 6), and
a deeper unspecialized layer, (Fig. 5, c). The two are
not sharply separated.

5. The contractile axis of the stem is a continuation of
the contractile layer of the ectosarc. Its upper end is dis-
tinctly striated or divided into a series of parallel, dark-
colored transverse bands, separated from each other by
mere transparent spaces.

c. The transparent, elastic cuticle (Fig. 4, ?, and
Fig. 5, a) covers the whole outer surface, and is thin
upon the disc and peristome ; thicker upon the bell, and
thickest in the stem. A very high power shows that its
surface is sculptured by parallel rows of fine dots. The
loose spiral, formed by the contractile axis of the stem, is
attached to the cuticle only on one side ; and when the axis
contracts the tubular cuticle is thus thrown into a spiral,
by the flattening of which the animal is drawn back to its
point of attachment. AYhen the contractile axis relaxes,
the elasticity of the cuticle straightens the stem, and
pushes out the body of the animal. When the peristome
and disc are retracted, the cuticle folds in with them, and
its elasticity causes the body to expand as soon as the
force is relaxed. The rapid contractions of the animal are
thus due to the contractile power of the outer layer of

18 HANDBOOK OF INVERTEBRATE ZOOLOGY.

ectosarc, while the more gradual extension is due to the
elasticity of the cuticle.

X. Make a sketch showing as many of these points as
possible.

XI. The Digestive Organs.

The solid particles of food are taken directly into the
endosarr, as they are in Paramcecium and Amn-ba ; but the
apparatus for the ingestion of food is quite complicated.
It can be examined to the best advantage in specimens
which have been fed with finely-powdered carmine or in-
digo. In such a specimen notice : —

a. The currents produced by the cilia of the peristome
and disc. These cilia act in such a way as to drive some
of the particles into the vestibule.

b. When the vestibule becomes filled with the colored
particles, it is seen to be continuous with a horizontal
tube, the G?.S-O/>/"'.'/"-S' (Fig- 4, e), which runs under the
disc into the endosarc.

1 . Notice that the walls of the oesophagus are covered
with small cilia, which keep the particles in motion, and
tend to drive them towards the inner end.

2. Notice that some of the particles are drawn out of
the vestibule and thrown away from the body, and a vio-
lent contraction of the peristome and disc occasionally
drives all the particles out of the oesophagus.

3. In very favorable specimens, the oesophagus and
vestibule may be seen to be lined by a continuation of the
cuticle.

4. At the inner end of the oesophagus is a small, slightly
dilated crop, which is also ciliated and lined by the cu-
ticle.

5. As the particles of food are drawn from the oesopha-
gus into the crop, the cilia of the crop give them a whirl-

VORTICELLA. 19

ing motion, and thus gradually aggregate them into a
little food ball.

6. From time to time the contractions of the body drive
these pellets into the endosarc, where they form food
vacuoles.

7 . As the currents of the endosarc carry the food vaeu-
oli around the body, the water and soluble portions are
digested out and absorbed, and the indigestible portion
is finally accumulated near the upper surface of the crop,
into which it is finally drawn by a contraction of the body,
to be expelled through the vestibule.

c. Make a sketch showing these points.

XII. As a rule only one contractile vesicle is present
near the upper end of the bell. It presents no features
which cannot be studied to better advantage in Paramce-
cium.

XIII. The endoplast is rather difficult to find in a liv-
ing specimen ; but it may be rendered visible by adding
a drop of dilute acetic acid to the drop of water which
contains the animal. It is a long, curved, club-shaped
body (Fig. 4, h), which extends around two-thirds or
more of the circumference of the body, and lies between
the ectosarc and endosarc, as shown at c in Fig. 5. It is
transparent, dark-colored, finely granular. There is no
endoplastule as there is in Paramcecium.

IV. THE MULTIPLICATION OF VORTICELLA.

THE beginner cannot hope to overcome the difficulties
which attend the attempt to trace all the stages in the life-
history of an Infusorian ; but a little patience will enable
him to find isolated examples of most of the points which
are to be noticed.

20 HANDBOOK OF INVKKTKHRATE ZOOLOGY.

I. The Multiplication by Fission.

a. Occasionally a Vorticella becomes permanently re-
tracted, and the body becomes lengthened laterally ; the
peristome gradually disappears ; the nucleus becomes
more conspicuous ; the food vacuoles and granules gradu-
ally disappear; the sarcode becomes transparent; and,
after a time, the nucleus assumes a position at right .-in-
gles to the stem, and the body shows traces of a vertical
division into two, as shown in Fig. 7.

b. The nucleus soon divides into two portions, which
separate from each other to become the nuclei of the two
new animals. (Fig. 8).

c. The constriction next becomes more marked, and at
or near each end of the long axis of the compound body
a curved groove makes its appearance. This groove soon
shows traces of ciliary action, and becomes converted into
the peristome of one of the new animals.

d. The animals then become completely separated, as
shown in Fig. 9. They assume the vase-like shape.
The peristomes and discs become fully developed, and two
perfectly-formed Vorticellae are now mounted upon a sin-
gle stem.

e. The stem gradually becomes forked.

f. Each of these animals may soon repeat the same
process of division, thus building up a community by re-
peated fission.

II. The Formation of the Free Form.

a. Sometimes, after the completion of the division, one
of the new animals is smaller than the other, and is situ-
ated nearly at right angles to the common stem.

b. This soon develops a crown of cilia around the fixed
end of the body, as shown in Fig. 10.

c. It then detaches itself from the stem by violent
movements, and swims away by means of its cilia.

VORTICELLA.

d. It soon loses its peristome and disc, and assumes
the form shown in Fig. 11, the end which now carries
cilia being that which was attached to the stem.

FIGS. 6, 7, 8, 9, 10, 11, and 12.

FIGS. 6-12. — Multiplication of Vorticella nebulifera. (Slightly altered
from Everts. )

FIGS. 6, 7, 8, 9. — Stages in the process of multiplication by fission.
FIGS. 10, 11. — The formation of a free individual.
FIG. 12. — The process of conjugation.

III. The Process of Conjugation.

a. After swimming about for a time, it fastens itself,
by what was originally its upper or peristomal end, to the
side of the body of one of the ordinary fixed animals.

b. The two then gradually become fused into one body,
as shown in Fig. 12. This process is essentially a process
of sexual reproduction, in which the entire bodies of the
two conjugating animals correspond to the two reproduct-
ive elements of one of the higher animals or plants. The
compound body formed by their union corresponds to a
fertilized egg or seed ; and it soon begins to multiply
again by division, although the precise method in which
division takes place, after conjugation, varies greatly in
different species of Vorticellidre.

IV. Specimens may sometimes be found which have

22 HANDBOOK OF IN\ Ki; I I.HKATE ZOOLOGY.

retracted the peristome and disc, and have secreted a
thick layer of cuticle, or a cyst, around the spherical body.
They sometimes become encysted while on a stem, or they
may separate from the stem tirst. The encysted forms
may retain their vitality for an indefinite period with-
out food or moisture. Encystment sometimes takes place
after conjugation, and sometimes apparently without con-
jugation.

V. CALCAREOUS SPONGE.

(Grantia [Sycandra] ciliata).

THE comparative simplicity of the structure of this
sponge (Grantia ciliata) renders it peculiarly available
for laboratory work.

It is a small, light-brown, nearly cylindrical, calcareous
sponge, from half an inch to an inch long. Isolated indi-
viduals are sometimes found, but it is more frequently
found in small crowded clusters ; and each large sponge
usually carries smaller ones, which have been formed as
buds around its base.

It is quite common on the New England coast, in shaded
places, at or near the low-water mark, upon piles, stones,
or shells, as well as upon other sponges, hydroids, and
tunicates.

The iponges should be placed in preserving fluid as
quickly as possible after they are collected, and, if it is
necessary to keep them alive longer than a few minutes,
they should be placed in as great a quantity of fresh sea-
water as possible, and kept shaded from the sun.

Some of the specimens should be preserved in alcohol,
to study the general form and the arrangement of the
calcareous skeleton ; and others should be preserved in
picric or chromic acid for histological work.

CALCAREOUS SPONGE. 23

The specimens which are to be preserved in alcohol
should be placed in seventy-five per cent alcohol as soon
as possible, and left for about twenty-four hours. They
should then be transferred to eighty or eighty-five per cent
alcohol, and left in that for about twenty-four hours, and
they may then be preserved, until they are wanted, in
ninety or ninety-five per cent alcohol.

The other specimens should be placed in a shallow pan
or dish filled with a saturated solution of picric acid, and
left for about ten hours. They should be transferred to
seventy-five per cent alcohol, in which they should be left
for about twenty-four hours, when they may be put into
strong alcohol ninety or ninety-five per cent. In about
twenty-four hours this alcohol should be poured off and
renewed ; and at the end of another day, if the alcohol has
turned yellow, it should be again renewed ; and so on,
until the alcohol remains colorless. Examine one of the
alcoholic specimens in a watch-crystal full of alcohol with
a hand-lens, or with a very low power of the microscope,
— ten or twenty diameters, and notice : —

I. The External Form.

a. The brown, cylindrical or vase-shaped body.

b. The opening, or osculum, at its distal or free end.

c. Smaller sponges, which have been formed by bud-
ding around the proximal end or base of the larger one.

II. Split the specimen with a razor or sharp scalpel
through the long axis of the body, thus laying open the
central cavity or cloaca. Examine the cut surface with a
very low magnifying power or with a hand-lens, and
notice : —

a. The body cavity, or cloaca (Fig. 13, </), a large
cylindrical cavity, which occupies the long axis of the

sponge-

UJ LI

HANDBOOK OF INVERTEBRATE ZOOLOGY.

b. The oKmlnm, or wide, round opening (Fig. 13, 6),
through which the cloaca communicates with the exterior.

FIG. 13. — Longitudinal
section of a calcareous
sponge (Sycandra ciliata)
magnified about ten diame-
ters. (Drawn from nature
by \V. K. Brooks.)

A. Mature sponge.
B. Bud. a. Crown of large
spicules around osculum.
b. Osculum. ft1. Osculum
of bud. c. Layer of spic-
ules. shown in a part of the
figure only. <1. Radiating
t ulics. shown in a part of the
figure only. e. Inner or
cloacal apertures of the ra-
diating tubes, shown in part
of the figure only. /. Sponge
flesh. (/. Cloaca. gl. Cloaca
of bud. fi. Base or attached
surface of sponge.

c. The wall of the
cloaca, as shown by
the section, is made
up of : —

1. An outer, brown
layer (Fig. 13, c),
which a slight magni-
fying power shows to
be made up of the pro-
jecting ends of the cal-
careous needles or spicules which form the skeleton of the
sponge.

2. An inner, nearly white, layer : the sponge-flesh (Fig.
13,/). This layer is somewhat thicker than the outer

CALCAREOUS SPONGE. 25

brown layer, except around the osculum, where it becomes
thin, and ends in a narrow edge.

d. The circlet of long, slender spicules, which forms
a collar or crown (Fig. 13, a) around the osculum.

e. The radiating tubes.

1. When slightly magnified, the inner surface of the
cloaca will be seen to be filled with small polygonal open-
ings (Fig. 13, e) the inner ends of the radiating tubes.
These are not as regular as they are represented in the
figure.

2. Upon the cut surface of the section of the sponge-
flesh along the sides of the cloaca, the radiating tubes will
be seen to be laid open longitudinally (Fig. 13, d}.
They are straight tubes, which penetrate the sponge-flesh
at right angles to the long axis of the body, and opening
on its outer surface, among the bases of the spicules,
establish a communication between the outer surface and
the cloaca.

f. Around the base of the sponge, notice the buds which
are to give rise, by their detachment, to separate sponges ;
and observe, —

1. The cloaca of the bud (Fig. 13, <?), which is in free
communication with the cloaca of the large sponge.

2. The osculum, spicules, and radiating tubes of the
bud, similar in every respect to those of the large sponge.

3. Notice that there is no boundary line between the
sponge-flesh of the large sponge and that of the bud.

t g. Make a sketch showing all these points.

III. The spicules. Cut a small piece from the speci-
men, and boil it for a short time in a test tube in caustic
potash solution, in order to separate and clean the spic-
ules. Allow them to settle to the bottom of the tube, and
then draw up some of them with a medicine dropper, and

26 HANDBOOK OF INVERTEBRATE ZOOLOGY.

placing them upon a slide, examine them with a magnify-
ing power of 200 or 300 diameters, noticing : —

a. Great numbers of tri-radiate spicules, formed by
three branches of about equal length, which meet at equal
angles of 120°.

b. Long unbranched, slender, pointed, needle-like spic-
ules.

c. Occasionally a second kind of tri-radiate spicule,
formed by the union of a short branch to the middle of a
long branch at right angles.

d. Make sketches of the spicules.

e. Wash them thoroughly with water, to remove all
traces of the caustic potash, and add to the drop of water
which contains them a drop of acetic or sulphuric acid.
They soon disappear with active effervescence.

IV. Imbed half the sponge in paraffine in position for
cutting longitudinal sections, and the other half for cutting
transverse sections. Tolerably satisfactory sections may
be cut from a sponge which, after being placed for about
a minute on a piece of blotting-paper to absorb the alco-
hol, is allowed to harden in a small quantity of melted
paraffine ; but much more satisfactory sections may be
obtained in the following manner : Place the sponge in
absolute alcohol for about an hour and then lay it on
blotting-paper to absorb the alcohol, and then place it in
a dish large enough to hold ten or more times its volume.
Fill the dish with turpentine, and add all the paraffine the
turpentine will dissolve, and keep in a warm room for ten
or twelve hours. Then melt some paraffine over a water-
bath, and place the sponge in it, and keep it at the melt-
ing point for three or four hours. Fold the corners of a
piece of writing-paper so as to form a box about an inch
long, and half an inch wide and deep. Place the sponge

CALCAREOUS SPONGE. 27

in the box, fill with the hot paraffine, and allow it to cool.
Cut a number of sections as thin as possible across the
imbedded sponge with a sharp razor, and transfer them to
a glass slide. Cover them with a mixture of equal parts
of carbolic acid and turpentine to dissolve away the par-
affine. After the sections become transparent, remove as
much as possible of the carbolic acid and turpentine with
a piece of blotting-paper, and cover them with a drop of
Canada balsam, and cover with a thin glass cover. The
balsam should be kept in a wide-mouthed bottle, loosely
covered by a perforated cork, through which a glass-rod
has been passed, and it should be taken up on the rod,
and thus transferred to the slide. If the balsam is too stiff
to drop readily from the rod, it may be liquefied by adding
a small quantity of benzole. The carbolic acid and tur-
pentine should also be kept in a bottle with a glass rod
passed through the cork.

a. Examine the longitudinal sections with a power of
two or three hundred diameters, and note : —

1 . The cut sections of the radiating tubes ; circular when
cut perpendicular to their long axis.

2. The more common kind of triradiate spicules ar-
ranged around, and in the spaces between, the tubes.

3. The long needle-like spicules upon the outer surface.

4. Make a sketch of a longitudinal section.

b. Examine a transverse section with the same power,
and notice : —

1. The radiating tubes (Fig. 14, b, 6, b) laid open
longitudinally. Each tube is divisible into three regions :

(i.) The narrow, inner aperture, through which its cav-
ity communicates with the cloaca.

(ii.) The long cylindrical canal, which traverses the
sponge-flesh from its outer surface to the cloaca.

HANDBOOK OF INVERTEBRATE ZOOLOGY.

(iii.) The small aperture or inhalent pore (Fig. 14, #),
through which the tube opens on the outer surface of the
sponge.

(iv.) Occasionally two radiating tubes communicate
through an opening in the wall between them.

FIG. 14. — Tranverse section of a calcareous sponge (G-rantia ciliate)
magnified about two hundred and fifty diameters. The section shows the
cavities of four radiating tubes. The spicules are represented in the
three on the left, and the cells, nuclei, and eggs, are shown in the one on
the right.

a. Cloaca, b, b, b, b. Cavities of the radiating tubes, c, c, c, c', c'. Tri-
radiate spicules projecting into the cloaca, d. The syncitium. e. Skele-
ton of tri-radiate spicules around the tubes. /. Long needle-like spicules.
g. Inhalent pores. L Eggs.

2. The needle-shaped spicules (Fig. 14, /), which are
arranged in bunches or stacks over the inhalent pores.

CALCAREOUS SPONGE. 29

3. The tri-racliate spicules (Fig. 14, e), which form a
framework or skeleton between the tubes.

The second, or more rare kind of tri-radiate spicules
(Fig. 14, e), which are placed around the wall of the
cloaca in such a way that the short branch of the spicule
projects into the cavity of the cloaca.

4. Make a drawing showing these points.
V. Histological structure.

Most of the following points may be made out in a speci-
men prepared as above, but they are more satisfactorily
shown in stained sections of a specimen wrhich has been
hardened in picric acid.

As eosin is a very convenient staining fluid, which
brings out the points to be noticed with sufficient clear-
ness, the sponge may be placed for half an hour in a very
dilute solution of eosin in water. It should then be
returned to absolute alcohol for a few minutes, and then
imbedded in paraffine, as above described. Cut a number
of transverse sections, mount them in balsam, and examin-
ing them with a power of three or four hundred diameters,
notice : —

a. The syncitium, or granular protoplasm (Fig. 14, d, d),
with scattered nuclei, which covers the outer surface of the
sponge, and lines the cloaca, and also tills the spaces be-
tween the radiating tubes. On the side of the cloaca it
extends, as a thin web, to the tips of the spicules, which
project into the cavity.

b. The layer of cellular epithelium, or endoderm (Fig.
14, 1i) which lines the radiating tubes. With a high
power, in favorable specimens, each cell may be seen to
carry a single long cilium.

c. The remains of the spicules imbedded in the synci-
tium.

30 HANDBOOK OF LN \ KI.'TKIJKATE ZOOLOGY.

d. The large granular oval eggs (Fig. 14, i) which lie
in the partitions between the radiating tubes, under the
layer of endodenn.

VI. THE STRUCTURE AND GROWTH OP' THE
ASEXUAL FORM OF A CAMPANULARIAN
IIYDROID.

(Eucope obliquu).

ALTHOUGH this description was written from a specimen
of the above species, almost any Campanularian Ilydroid
may be used to verify the points, since the difference!
between them are slight.

They may be found in abundance, in the form of brown
moss-like tufts, near low-tide mark, on plants and stones.
on the lower surfaces of overhanging rocks, on the timbers
of wharves, the bottoms of boats, or on floating drift-wood
or algae.

The living animals should be examined in sea-water, as
it is difficult to preserve satisfactory specimens. If speci-
mens are to be preserved for laboratory work, select those
which are as clean and free from foreign matter as possi-
ble, and plunge them, alive, into a saturated solution of
picric acid in fresh water. In three or four hours they
may be transferred to seventy-five per cent alcohol, or to
a mixture of equal pails of alcohol, glycerine, and sea-
water. After about twelve hours the specimens which
have been placed in alcohol may be transferred to ninety
per cent alcohol for permanent preservation.

I. Examine with a low power a portion of a living
colony in a watch-crystal of sea-water, or a portion of a
preserved specimen in a small quantity of the preserving
fluid, and notice : —

32 HANDBOOK OF INVEltl KI5KATE ZOOLOGY.

FIG. 15. — Hydranths, reproductive calyces and medusae of an unde-
scribed species of Eucope, matjnilied about fifty diameters, from a living
specimen. Drawn by \V. K. Brooks.

A. A, A. Hydranths or nutritive zooids.

B. A reproductive calycle, showing the blastostyle and very young
medusa-buds.

C. An older reproductive calycle. with fully-formed medusae.

Z>. View of the lower or oral surface of a young medusa, a few min-
utes after its escape from the reproductive calycle.

E. Side view of same.

F. Medusa about an hour older.

G. Side view of medusa, about thirty-six hours after its escape from
the reproductive calycle.

a. Perisarc. b. Endosarc. c. Tentacles of hydranth. <j. Manubrium.
h. Body of hydranth.

a. The vase-shaped, tentaculated, nutritive zooids, or
hydranths (Fig. 15, A, A, A).

b. The branched stem, or hydrocaulus by which they
are united to each other, and to a common base, or hydro-
rhiza.

c. The transparent chitinous shell, or perisarc (Fig.
15, a) which covers the hydrorhiza, the hydrocaulus, and
portions of the hydranths.

d. Make a sketch of these points, showing also the
arrangement of the hydranths upon the hydrocaulus.

II. Examine a portion of a colony with a higher power,
and note : —

a. The transparent cylindrical sheath of perisarc (Fig.
15, a) which is annulated above and sometimes below the
points where the hydrocaulus divides.

b. The coenosarc or fleshy axis (Fig. 15, b) which
occupies the cavity of the tube, and is loosely attached at
intervals to its inner wall. In favorable specimens it will
be seen to consist of three layers.

1. The outer layer, or cctml^rm consists of somewhat
transparent cells with large nuclei, and forms the outer
surface of the coenosaiv.

CAMPANULARIAN HYDKOID. 33

2. The inner layer, or endoderm, is of about equal
thickness, but the cells which compose it are more opaque
and granular.

3. A thin transparent supporting layer with well-defined
edges will be seen to separate the outer from the inner
layer.

c. In the centre of the coenosarc notice the tubular
body cavity.

d. In a living specimen note that the granular matter
which fills the cavity is kept in circulation by the action
of cilia which arise from the inner surface of the endo-
derm.

e. Make a sketch showing these points.

III. Examine the hydranths, and having found one
which is expanded, note : —

a. The open cup or vase, the hydrotheca (Fig. 15, a')
formed by the expansion of the perisarc.

b. The crown of tentacles (Fig. 15, c) arranged in a
circle.

c. The rounded prominence, or manubrium (Fig. 15, g)
which projects into the space between the tentacles, and
carries the mouth upon its free end.

d. The body (Fig. 15, h) of the hydranth, made up
like the stem of three layers.

1. The thin transparent ectoderm.

2. A sharply-defined supporting layer.

3. A very thin layer of entloderm, made up of large
opaque vacuolated cells, the inner or free ends of which
carry cilia.

e. Notice that the body cavity of the hydranth is sim-
ply an enlargement of that of the hydrocaulus. It is
lined with cilia, and the particles of food which it usually
contains may in the living specimen be seen to circulate
through the stem.

HANDBOOK OF INVERTEBRATE ZOOLOGY.

f. Make a drawing of a hydranth, showing all these
points.

IV. Examine a tentacle with a higher power, and notice
that it is made up, like the hydroraulus and hydranth, of
three layers.

a. The ectoderm forms a thin, highly clastic, and con-
tractile layer (Fig. 19, «) which contains numbers of
small oval bodies, the nematocysts or lasso cells.

b. The supporting layer (Fig. 19, b) forms a thin
transparent line between the ectoderm and endoderm.

c. The endoderm (Fig. 19, c) completely tills the
centre of the tentacle, and consists of large cells with
a distinct cell wall and a large granular central nucleus,
which is attached to the wall by irregularly branched
protoplasmic threads.

-^ F i<;. 10. Part of a tentacle, magnified two hundred and

fifty diameters.

a. Ectoderm. 6. Supporting layer, c. Endoderm.

d. In a surface-view notice the longitudinal
muscular fibres, which lie just outside the sup-
porting layer of the tentacle.

e. In a living specimen notice that the tenta-
cles are retracted and extended by contractions
of the elastic substance of the body, and not by
the folding of the tentacle upon itself.

f. Make a drawing of a tentacle, showing these
points.

g. Crush a portion of a tentacle, by pressure
on the cover-glass, and examining it with a high
power, notice the nematocyst* which are thus set
free. When fully extended, each (Fig. 20) con-
no, in. gjstg Qf a sma]i ova] capsule, and a very long

slender filament, with three barbs or hooks near its prox-
imal end.

CAMPANULARIAN HYDROID. 35

V. Search among the tips of the branches of a colony
for the various .stages in the process of formation of a
hydrant h by budding, ,

and notice : —

a. A stage in which
the bud is a simple,

n earl y cylindrical **•

knob at the end of a FlG'20-

branch (Fiij. 16). The FlG' 2(X ~~ A discharSed nematocyst, mag-
nified three hundred and fifty diameters.

coenosarc is in contact

with the thin investing layer of perisarc (Fig. 16, a),
and its distal end is made up of a thick layer of ectoderm
(Fig. 16, b) and a mass of loose endoderm cells (Fig.
16, c). At a very early stage the cavity of the stem does
not extend into this muss.

b. A stage in which the bud (Fig. 17) is club-shaped,
— the perisarc at the tip of the stem very thin, while the
ectoderm is very thick. The body cavity (Fig. 17, d)
no\v extends into the bud, and the endoderm cells
(Fig. 17, c) form a true inner layer. The coenosarc
has begun to separate from the perisarc at the sides, and
the outline of the body of the hydranth can be recog,-
nized.

c. In a more advanced stage (Fig. 18) the shape of
the body is well marked, and the coenosarc is more free
from the perisarc, which still entirely covers it.

d. In a more advanced stage the perisarc is ruptured
and expanded to form the hydrotheca, and the manubrium
and budding tentacles can be seen.

e. Make a sketch showing the various stages in the pro-
cess of budding.

f. Notice that in the living specimen the particles of
food are carried through the hydrocaulus into the body

HANDBOOK OF INVERTEBRATE ZOOLOGY.

cavity of the bud long before this has a mouth of its
own.

FIG. 16.

FIG. 17.

Fi<;. is.

FIGS. 16, 17, and 18. — Three stages in the formation of a hydranth by
budding, magnified one hundred and fifty diameters. (Drawn from na-
ture by W. K. Brooks. )

a. Perisarc. b. Ectoderm, c. Endoderm. d. Body cavity.

VI. Place a small healthy colony in a good supply of
fresh sea-water, and cutting some of the hydranths and
buds from the tips of the stems with a sharp pair of scis-
sors, trace their reproduction by a process which is very
similar to the normal method of budding. During the
experiment, which occupies several days, the water should
be changed frequently, and it may require three or four
days for the colony to become sufficiently accustomed to
its confined life to commence the process.

Confinement in too small a quantity of water often
causes certain abnormal change- which may be noticed.

OCELLATE HYDRO-MEDUSA. 37

The hydranths drop off, and the tips of the branches grow
very rapidly, sending off long contorted transparent pro-
longations.

By changing a specimen from a small quantity of water
to a larger quantity, the hydranths can be made to grow
again, and this process can be repeated several times.

VII. THE STRUCTURE OF AN OCELLATE HYDRO-
MEDUSA.

(Mnemopsis Bachei.)

As the small size and flat shape of the medusa stage of
the hydroid described in the last section render it some-
what unfavorable for laboratory work, the student should,
before studying it, make himself acquainted with the
structure of one of the larger hydro-medusas.

The species which is shown, magnified ten diameters, in
Fig. 21, is very abundant during the summer along the
Atlantic coast, and it is therefore a good form to select for
study. Specimens may usually be procured by dipping
at the surface of the ocean on quiet evenings with a sur-
face-net. The net should be made of medium bolting-
cloth, and should be about three inches deep, with a wire
rim about six inches in diameter, fastened to a short
handle. In using it, fill a bucket about half-full of fresh
sea-water, and after dipping or skimming gently along the
surface of the ocean for about a minute, insert the net into
the bucket, and wash it in the nvater to dislodge any me-
dusre which have adhered to it. This process of dipping
and washing should be kept up for an hour or more ; and
in washing the net, care should lie taken that the rim does
not dip below the surface of the water in the bucket, as
valuable specimens might thus be dipped out of the bucket
and thrown away.

38 I!AM>];<)OK OF INVKIITKI'.IIATK /.< ;< >L< >! ;y .

The most favorable time for all kinds of surface-collect-
ing is a calm evening, when the water is phosphores-
cent ; and in most localities, especially on low sandy
coasts, a greater variety of forms will be met with at high
water than at other times.

After the bucket with its contents has been carried
home, a small quantity of the water should be dipped up
in a small beaker or a tumbler with smooth sides, and held
before a light for examination. The collection will proba-
bly be found to contain numbers of small rounded nearly
hemispherical transparent medusa?, and these may IK;
picked out with a dipping-tube and preserved for examina-
tion in small aquaria or beakers of fresh sea-water.

Most of the points in this description may be made out
by the examination of living specimens, but they may IK;
preserved for winter work if necessary. The most satis-
factory method of preservation for microscopic examina-
tion is by the use of osinic acid. The specimens to be
preserved should be placed alive in a large watch-crystal
full of sea-water, and to this fifteen or twenty drops of one
percent solution of osmic acid in distilled water should be
added.

As soon as the specimen begins to turn dark, which will
be in live or ten minutes, pour off the water and fill the
watch-crystal with new sea-water, and pour this oil' in live
or ten minutes and renew once more. This should be
done several times to wash out all traces of the acid. The
specimen may then be strained in dilute piero-earmine
for about an hour, and it may then be preserved in a mix-
ture of equal parts of ninety-five per cent alcohol, sea-
water, and glycerine. If osmic acid cannot be procured,
satisfactory specimens can be preserved with picric acid.
The specimens should be placed in a flat-bottomed dish

OCELLATE HYDRO-MEDUSA. 39

filled with a saturated solution of picric acid in fresh
water, and left for eight or ten hours. Each specimen
should then be placed, by itself, in a small bottle of very
dilute alcohol ; about forty per cent. In about half an
hour this should be poured off and renewed, and the pro-
cess repeated until the alcohol shows no trace of a yellow
color. After the specimen has remained for about half
an hour in the last alcohol, pour off all but enough to
cover it, and add strong alcohol, a few drops at a time,
at intervals of about five minutes, until the bottle is
filled.

The specimen should be examined in some of the fluid
from its own bottle.

I. The General Structure. Examining a specimen in a
watch-crystal, with a low power of the microscope, or
with a hand-lens, notice :

1. The transparent gelatinous umbrella (Fig. 21, ft,
25, a) which makes up the greater part of the body. The
outlines are sharp and regularly curved in a living speci-
men, but they are usually somewhat shrunken and dis-
torted in a preserved specimen.

a. The portion of the umbrella which is at the top in
Fig. 21. and which, from its relation to the mouth, may
be called the ab-oral portion, is greatly thickened, and the
outer and inner surfaces are separated from each other by
the elastic gelatinous substance of the umbrella.

b. At the lower or free edge (Fig. 21, b), the gelatin-
ous substance gradually diminishes in thickness.

2. The sub-umbrellar cavity or space (Fig. 25, b) under
or inside of the umbrella.

3. The velum, or muscular horizontal diaphragm (Figs.
21 and 25, c) which runs inwards around the lower edge
of the umbrella, over the opening of which it forms a flat

HANDBOOK OF INVERTEBRATE ZOOLOGY.

partition, which reduces the external opening of the sub-
umbrellar cavity to a small circle (Figs. 21 and 25, d).
This opening varies in size according to the degree of ex-
pansion or contraction of the velum.

FIG. HI

FIG. 21. — Mnemopsis Bachei (southern variety) drawn from a living
specimen, magnified about ten diameters. (Drawn from nature by W. K.
Brooks. )

a. Umbrella, b. Sensory bulb. c. Velum, d. Aperture of velum.
c. Club-shaped tentacles. /. Manubrium. g. Oral tentacles, i. Radiat-
ing chymiferous tubes, k. Circular chymiferous tube. I. Reproductive
organs, h. Radial tentacles.

4. The four bunches of radial tentacles (Furs. 21 and
25, h) which spring from the lower margin of the umbrella,
outside the velum. In the living medusa these tentacles
are very extensile, and their length may be equal to or

OCELLATE HYDRO-MEDUSA. 41

greater than the diameter of the umbrella, but in preserved
specimens they are usually much contracted.

5. The stomach, or manubrium (Figs. 21 and 25, /)
which is suspended from the inner surface of the umbrella,
or sub-umbrella, and hangs down into the sub-unibrellar
cavity. The manubrium consists of:

a. Four dichotomously-branched oral tentacles (Figs.
21 and 25, g), upon the manubrium.

b. The mouth, an opening situated between the bases
of these tentacles, and serving to put the cavity of the
manubrium into communication with the cavity of the sub-
umbrella.

c. The body, or manubrium proper, with its central
cavity, or stomach.

6. The chymiferous tubes: a set of prolongations of the
stomach into the substance of the umbrella. This system
consists of four- radial tubes, and a circular tube.

</. The four radiating chymiferous tubes (Figs. 21 and
25, z) run outwards and downwards from the point where
the manubrium hangs from the sub-umbrella, and they
may be traced down to the free edge, just above the inser-
tion of the velum. They lie near the sub-umbrcllar sur-
facc, but they are entirely surrounded by the gelatinous
substance of the umbrella. Observe that they are equi-
distant and separated from each other by an arc of
ninety degrees. Observe, too, that each of them lies
in the same place with one of the bunches of radial ten-
tacles.

b. The circular chymiferous tube (Figs. 21 and 25, A1)
runs around the free edge of the umbrella just above the
insertion of the velum.

c. Notice that the radiating tubes open into the circular
tube, so that the whole system is in direct communication

42 HANDBOOK OF INVERTEBRATE ZOOLOCY.

with the stomach. In a living specimen the system of
tubes and the cavity of the manubriiim are ciliated and
particles of partially-digested food maybe seen circulating
through them.

7. The i->-jtro(fi>cfir>' oi-f/cnis : four long, crenated, opaque,
ribbon-like bodies (Figs. ~2\ and '!'), 1} between the inner
surfaces of the radiating ehymiferous tubes and the sub-
umbrella.

8. The ocelli : dark pigment spots, at the bases of the
radial tentacles.

!». Lay a specimen open by a cut, with a sharp razor.,
through the umbrella and the long axis of the manubrium,
and examine again in this longitudinal section all the struc-
tures which have been described.

10. Make a drawing showing all these points.

11. Study the manner in which the living animal
moves through the water, by contractions of the um-
brella.

II. The more minute details of structure may most of
them be made out by the examination of a living specimen
with high powers, but it is much better to use preserved
specimens, as the active movements of the living animal
render careful observation difficult. If working at the
seashore, place a living specimen in a watch-crystal of sea-
water, and add lift ecu or twenty drops of one per cent
solution of osmic acid. As soon as the specimen begins
to turn dark, which will be in two or three minutes, pour
off the water, and wash the specimen several times in fresh
sea-water, to get rid of all traces of the osmic acid. Stain
it for about half an hour in very dilute picro-carmine, and
then place it in a fluid composed of one-third glycerine
and two-thirds water, and with a sharp pair of scissors cut
oft' one of the bunches of radial tentacles, and mount it

OCELLATE HYDRO-MEDUSA.

on a glass slide with a thin glass cover, in a. drop of the
dilute glycerine, and examine it with a magnifying power
of one hundred and tifty to three hundred diameters. If
osmic acid cannot be procured, mount in the same wny a
portion of a specimen which has been preserved in picric
acid, as already directed.

1. Observe that the
tentacles (Fig. 22, K

a, a, (i) are arranged in
pairs on the sides of the
plane of one of the ra-
dial cliymiferous tubes.

The number increases
with age, and those near-
est the middle are the
oldest.

FIG. 22. — Sensory bulb, and
bunch of radial tentacles, from
a living specimen, magnified
about eighty diameters. ( Drawn
from nature by W. K. Brooks. )

a. Club-shaped tentacles.
a'o"ii'". Extensile tentacles.
/. Sensory bulb. g. Circular
cliymiferous tube. h. Radiat-
ing cliymiferous tube.

PIG. 22.

2. The pair nearest the median line (Fig. 22, «) are
somewhat different from the others. They are shorter,
less contractile, and are made up of an enlarged base which
carries an ocellus, a slender shaft, and an enlarged, club-
shaped terminal portion.

3. The ocellus at the base of this tentacle is a spherical
accumulation of pigment granules, in the centre of which
is a transparent, highly refractive spherical lens.

44 HANDBOOK OF INVERTEBRATE ZOOLOGY.

4. The other tentacles are much larger, and are capable,
in the living animal, of great extension and retraction ;
each will lie found to be made up of: -

a. A central axis of endoderm cells, arranged in a sin-
gle row.

b. A transparent supporting layer, which surrounds the
endoderm cells, and may be seen in optical section, as a
well-defined transparent band on each side of the endo-
dermal axis. •

c. The layer of longitudinal muscular fibres, which lies
just outside the supporting layer.

d. The thin layer of ectoderm which forms the outer
surface of the tentacle, and is filled with nematocysts.

5. The ocelli at the bases of these tentacles are some-
what smaller than those on the club-shaped tentacles, and
the lenses may be absent.

6. The sensory bulb. The tentacles do not spring
directly from the edge of the umbrella, but are carried
upon a somewhat triangular enlargement, the sensory bulb
(Fig. 22,/).

This is an enlargement of the margin of the umbrella,
at the point when; a radiating chymiferous tube (Fig.
22, /<) joins the circular tube g. The cavity of the bulb is
filled by an enlargement of these tubes which sends diver-
ticula off towards the bases of the tentacles, and is marked
by dark pigment.

7. In the cut ends of the chymiferous tubes notice the
large opaque granular endoderm cells which line them.

III. The mouth tentacles. Cut, off one of the branched
mouth tentacles : mount it in the same way and examine
it, first with a low power, and then with a higher power.

1. With a low power notice that the main trunk divides
into two equal branches, and each of these again into two,

OCELLATE HYDRO-MEDUSA.

and so on (Fig. 23), until a great number of small ter-
minal branches is formed. Notice the round knobs at the
ends of the terminal branches.

2. Examine one of the main trunks
with a higher power, and notice : —

a. The double layer of large endo-
derm cells (Fig. 24, a) which forms the
solid axis of the tentacle.

FIG. 23.

FIG. 23. — An oral tentacle, magnified about
eighty diameters. (Drawn from nature by W. K.
Brooks. )

b. The supporting layer.

c. The muscular layer (Fig. 24, b).

d. The ectoderm, with a few scattered nematocysts.

FIG. 24.

FIG. 24. — The tips of two branches of an oral tentacle, magnified
two hundred and fifty diameters, from a picric acid specimen. (Drawn
from nature by W. K. Brooks. )

a. The endoderm cells, b. The muscular layer, c. Battery of nema-
tocysts.

46 HANDBOOK OF. INVERTEBRATE ZOOLOCV.

3. Examine the hull) at the tip of one of the branches,
and notice that the endoderm i.s wanting here, while the
greiitly thickened ectoderm is packed with large nema-
tocysts.

IV. Cut off a portion of the nianubrimn. and tea/ing it
out in a drop of glycerine, notice the large granular endo-
denn cells which line its cavity, the transparent ectoderm
cells which cover its outer surface, and the supporting l.-iyer
i >et ween the two.

V. Examine the inner surface of a piece of the umbrella,
and notice : —

1. The scattered nuclei of the greatly-flattened ecto-
derm cells which cover it.

2. Under these the layer of longitudinal mu-cular fibres
which encircles the sub-umbrella, and which, by its con-
traction, drives the water out of the cavity, through the
opening of the velum.

3. Here and there a dark brown stellate ganglion cell,
which consists of a central body with a nucleus, and two
or three long, fine, radiating nerve-fibres.

4. Along the lines of the radiating chymiferous tubes,
notice a second layer of muscles, perpendicular to the
circumference of the umbrella.

VI. Examine a piece of the velum, and notice : —

1. An outer layer of cells, continuous with those upon
the outer surface of the umbrella.

2. An inner layer, continuous with those on the sub-
umbrellar surface.

3. A thin, transparent, supporting layer, separating these
two layers of cells.

4. The muscular layer of the velum, between the sup-
porting layer and the inner layer of cells.

VII. The nerve-ring. Examine a piece of the lower

OCELLATE HYDRO-MEDUSA. 47

edge of the umbrella, and on its outer surface, just above
the insertion of the velum, notice a dark-colored band
(Fig. 25, m), which encircles the body parallel to, but
just outside of and below, the circular chymiferous tube.
In favorable specimens this band may be seen to consist
of:-

1. A surface-layer of thickened ectoderm cells, with
cilia upon their outer surface.

2. An inner layer of nerve-fibres, with a few scattered
ganglion cells like those of the sub-umbrella.

VIII. Examining pieces from various parts of the body,
trace out the general relations of the various layers which
have been noticed, and observe: —

1. The ectoderm (Fig. 25, 1). This covers the outer
surface of the umbrella, the radial tentacles, the outer sur-
face of the velum, the inner surface of the velum, the
sub-umbrella, the outer surface of the manubrium, and
the outer surfaces of the mouth tentacles.

a. On the outer surface of the umbrella the ectoderm
cells are very much flattened, and as they are easily
detached, they may not be present in a preserved speci-
men. In a specimen which has been recently hardened in
osmic acid, their nuclei may be seen in a surface-view of
the umbrella.

I). At the lower edge of the umbrella the ectoderm sud-
denly becomes thickened to form the ciliated epithelium
of the nerve ridge.

c. On the radial tentacles the ectoderm forms a thin
layer with nematocysts.

d. The outer and inner layers of epithelium of the velum
are continuous with each other at the free edge, and are
formed of thickened cells.

e. The ectoderm of the sub-umbrella is very thin, and
only the scattered nuclei can be recognized.

HANDBOOK OF INVERTEBRATE ZOOLOGY.

/. On *the manubrium the ectoderm cells are again
thickened, and have a few scattered nematocysts.

FIG. 25.

Fio. 25. — Diagram to show the arrangement of the layers of the body
of a Hydro-Medusa, as seen in a vertical section. The section is repre-
sented as passing through a radiating chymiferons tube on the right side,
and through the space between the tubes on the left.

a. Umbrella, c. Velum, d. Aperture of velum. <•. Cavity of sub-
umbrella. /. Manubrium. y. Oral tentacles. //. liadiul tentacle.
i. Radiating chymiferous tube. k. Circular chymiferous tube. I. Re-
productive organ, m. Sensory ridge.

g. The ectoderm of the mouth tentacles is very thin
except at their tips, where it forms a knob-shaped battery
of nematocysts.

2. The endoderm (Fig. 25, 2], This layer lines the
stomach and chymiferous tubes, and sends solid processes
out to the tips of the oral and radial tentacles.

CAMPANULARIAN HYDROID. 49

3. The supporting layer (Fig. 25, 3) separates the
endoderm from the ectoderm in the manubrium and in the
tentacles, and it also runs out between the two epithelial
surfaces of the velum.

VIII. THE MEDUSA STAGE OF A CAMPANULA-
RIAN HYDROID.

I. EXAMINE specimens of the hydroid which was de-
scribed in Section VI., until one is found which has repro-
ductive calycles (Fig. 15, B and (7). These will usually
•be found near the bottom of the hydrocaulus. Having
found a specimen, cut off the section of the stem which
carries the reproductive calycles, and place it upon a slide
under a cover glass, in a drop of sea-water, for microscopic
examination. Examining it with a low power, fifty to one
hundred diameters, notice : —

a. The gonangium, or capsule of perisarc (Fig. 15, d)
which corresponds in general outline and in its position
upon the stem, to the hydrotheca of one of the ordinary
nutritive hydranths, although it is longer, and is closed at
its free end.

li. The blastoslyle^ or rudimentary hydranth (Fig. 15, c) .
This consists of a long slender stem or axis, which cor-
responds to the body of one of the nutritive hydranths ;
and a club-shaped tip, or manubrium, with scattered
nematocysts.

There are no tentacles, and the manubrium has no ter-
minal orifice or mouth ; but the body layers wyhich have
been examined in the hydranth may be seen in the blasto-
style, and there is a central ciliated body-cavity, continu-
ous with the cavity of the hydrocaulus. In transparent
specimens particles of food may be seen to pass up the
stem into the blastostvle.

50 HANDBOOK OF INVERTEBRATE ZOOLOGY.

c. The medusa-buds (Fig. 15,/") arranged around the
blnstostyle. Those nearest its free end are the oldest and
largest, and when fully developed (Fig. 15, c) they almost
entirely fill the cavity of the gonangium. When ready to
be discharged each will be seen to be a flattened medusa,
with a number of marginal tentacles folded down over the
bottom of the umbrella (Fig. 15, i).

d. Make a drawing of a reproductive calycle, showing
these points.

II. The general structure of the medusa. Place two or
three stems, with ripe calycles, in a good supply of fresh
sea-water, and after a day or two, carefully examine it for
young medusa, which will be found swimming in the
water, usually at the surface. They are much smaller
than the medusa described in Section VII., and the nearly
flat, disc-shaped umbrella has tentacles around its entire
edge. In swimming the umbrella is usually carried turned
wrong side out, as shown in Fig. 15, E, with the manu-
brium projecting from the centre of the convex surface,
and the tentacles turned up at their bases, so as to point
towards the ab-oral surface.

a. If possible, notice the escape of a medusa from the
reproductive calyx. At the time of escape the tentacles
are folded down, as shown at i, but within a few minutes
they straighten, as shown at Z>, and in fifteen or twenty
minutes the medusa begins to swim actively, as shown at
E, by vigorous flaps of its tentacles. It grows rapidly,
and in about an hour it appears as shown at F.

b. Pick out one of the larger specimens with a dipping-
tube ; and placing it in a watch-crystal with sea-water,
examine it with a low power, noticing : —

1. The manubrium (Fig. 15, D and JE, &) with its
large terminal mouth, and stomach-cavity ; notice that the

CAMPANULAKIAN HYDKOIU. 51

edges of the mouth are entire, without lobes or oral ten-

tacles, in the younger specimen, but divided into four oral
lobes in older ones.

2. The radiating chymiferous tubes, which may be traced
from the base of the manubrium for a short distance to-
wards the free edge of the umbrella.

3. The flattened discoidul inverted umbrella.

4. The marginal tentacles. These vary in number, ac-
cording to the species, but they are always arranged equi-
distantly around the entire circumference of the umbrella.
There is always one, which may be called the radial ten-
tacle (Fig. 15, jF, 1) in the plane of each chymiferous
tube, and another, which may be called the median inter-
radial tentacle (Fig. 15, F, 2) midway between each two
radial tentacles. In the species figured there are always
two, and occasionally three between each radial tentacle
and the nearest median tentacle.

5. The otocysts. Eight small transparent spherical
vesicles, situated upon the oral faces of the bases of the
eight tentacles adjacent to the four median tentacles.

6. Examine larger specimens, which may usually be
obtained in abundance by dipping at the surface of the
ocean on calm evenings, and notice : —

a. The very numerous marginal tentacles.

b. The four deeply cleft oral lobes.

c. The four rounded reproductive organs which project,
beyond the outline of the sub-umbrella, one near the mid-
dle of each radiating chymiferous tube.

III. Kill a specimen with osmic acid, as directed in
Section VII., and after staining with picro-carmine, mount
it in dilute glycerine, and examine it with a high power —
two hundred to five hundred diameters — and notice : —

a. The ab-oral surface.

HANDBOOK OF INVERTEBRATE ZOOLOGY.

1. The ab-oral surface of the umbrella is covered by
large, flat, nucleated cells (Fig. 26, a) which are quite

FIG. 26.

FIG. 26. — Ab-oral surface of a young medusa of Eucope, about twelve
hours after its escape from the reproductive calycle; from au osmic acid
specimen, magnified about two hundred diameters. (Drawn from nature
by W. K. Brooks.)

a. Upper surface of umbrella. b. Edge of umbivll.i. c. T< :
d. Enlarged inner side of tentacles, e. Shafts of tentacles. /. Otocysts.

CAMPANULAltlAX HYDROID. 53

distinct in a young specimen, although in an old specimen
it is difficult to make out any thing more than their
nuclei.

2. Around the circumference of the umbrella there is
usually a prominent ridge (Fig. 26, b) produced by the
folding back of the tentacles.

3. The marginal tentacles (Fig. 26, c) are rather sharply
divided into an enlarged broad bulb (Fig. 26, d) and a
more slender cylindrical, slightly tapering shaft, e. In
the shaft notice : —

(i.) The very thin layer of ectoderm, which is thick-
ened at intervals to form annulations which are filled with
large neinatocysts.

(ii.) The longitudinal muscular fibres which lie under-
neath the ectoderm.

(iii.) The transparent supporting layer.

(iv.) The solid axis of large endoderm cells.

4. In the bulb at the base of the tentacle, notice : —

1. The thickened layer of large prominent rounded
ectoderm cells.

2. A large central endoderm cell.

b. The sub-umbrellar surface (Fig. 27).

1. The vase-shaped manubrium (Fig. 27, a) with a
wide opening, the margins of which are divided into four
lobes.

(i.) The line of nematocysts which fringes the mouth,
(ii.) The polygonal ectoderm cells which cover the
manubrium.

2. A nearly square stomach-chamber (Fig. 27, b) which
lies in the centre of the sub-umbrella, and is separated by
a somewhat contracted neck from the cavity of the manu-
brium.

3. The four radiating chymiferous tubes (Fig. 27, c)

HANDBOOK OF INVERTEBRATE ZOOLOGY.

which run off from the four corners of the stomach to-
wards the edge of the umbrella. These are very difficult

FIG. 27.

FIG. 27. — Oral surface of the same medusa. (Drawn from nature by
W. K. Brooks.)

a. Manubrium. b. Neck of manubrium. c. Radiating chymiferous
tubes, d. Reproductive organs, c. Enlarged bases of tentacles. /. Oto-
cysts. g. Velum. 1. Radial tentacles. 2. Median inter-radial tentacles.
S. Tentacles which carry otocysts.

•

CAMPANULARIAN HYDROID.

to trace in a young specimen, but more distinct in old
ones. The circular chymiferous tube is so small that it
can only be seen at all under the most favorable circum-
stances.

4. The reproductive organs (Fig. 27, d) on the lines of
the radiating tubes, about half-way between the centre and
edge of the umbrella.

5. The small epithelial cells which cover the surface of
the sub-umbrella.

6. The velum (Fig. 27, </) is very narrow, and is usu-
ally stretched over the bases of the marginal tentacles.

1. Notice the small, flat, epithelial cells which cover it,
and pass, by a gradual transition, into the rounded ' ecto-
derm cells which cover the bases of
the tentacles.

7. The auditory organs (Fig.
27, /) consist of a nearly spherical
capsule, attached to the outer sur-
face of the velum close to the base
of a tentacle, and containing a cen-
tral highly refractive, spherical oto-
lith.

IV. Examine one of the auditory
organs with a high power — five or
six hundred diameters — and no-
tice : —

FIG. 28. — Otocysts of Euchilota ventricu-
laris, magnified four hundred diameters; from
an osmic acid specimen. (Drawn from nature
by W. K. Brooks. )

a. Supporting layer, b. Outer layer of
epithelium, c. Inner layer of epithelium.
d. Otolith. e. Velum. /. Cavity of Otocyst. FIG. 28.

a. The capsule (Fig. 28). This consists of
layers.

56 HANDBOOK OF INVERTEBRATE ZOOLOGY.

1. A very delicate supporting layer (a).

2. An outer layer of cells (6), continuous with the
ectoderm cells of the outer surface of the velum.

3. An inner layer of cells (c), continuous with the ecto-
derm cells of the inner surface of the velum.

b. The otolith (d) is surrounded by a delicate layer of
protoplasm, by which it is attached to the inner surface of
the capsule.

c. Four or five fine sensory hairs project from the wall
of the capsule towards the otolith.

IX. STRUCTURE OF THE STARFISH.

( Aster acantheon beryiinus.)
THE HARD PARTS.

SPECIMENS of the common starfish may be found in
abundance at low tide at almost any point on our north-
ern coast, although on the more sandy southern coast it
may be necessary to dredge for them in deep water. The
ordinary oyster-dredge may be used, and specimens can
usually be obtained by dredging upon oyster-beds. Some
should be preserved in alcohol, and some dry. Those
which are to be kept in alcohol should be slit with the
point of a sharp knife along the upper surfaces of the
rays in order to allow the alcohol to penetrate them, and
they should then be placed in seventy-five per cent alco-
hol. This should be poured oft' and renewed within a week
or less, and replaced by fresh alcohol.

The specimens which are to be dried should be placed,
alive, in a flat-bottomed dish of warm fresh water, and
left for ten or fifteen minutes. They should then bo laid,
flat, in enough seventy-five per cent alcohol to cover them,
and in about an hour taken out and dried in the sun, or

STRUCTURE OF THE STARFISH. 57

by a fire, for about twelve hours. The dried specimens
should be used to study the hard parts, and the alcoholic
or fresh specimens for the internal structure.
1. In a dried specimen, notice : —

a. The central pentagonal disc, from which radiate five
arms, or rays.

b. The nearly flat actinal or oral surface.

c. The more convex ab-actinal or ab-oral surface.

d. Upon the oral surface, notice : —

1. The central pentagonal mouth.

2. The five clusters of spines, or mouth papillae, which
surround and project over the opening.

3. Five grooves or furrows, the ambulacra! furrows,
which radiate from the sides of the mouth along the oral
surfaces of the rays to their tips. The furrows are deep-
est and widest at their central ends, and decrease in size
towards the tips of the rays.

e. Make a sketch of the oral surface, showing these
points.

f. On the ab-oral surface, notice : —

1. The integument^ or perisoma, made up of an irregu-
lar network of calcareous ossicles carrying short blunt
spines. The spaces between the ossicles are filled by a
soft flexible membrane. Along the middle of the ab-oral
surface of each ray the spines form an indefinite line. f

2. Near one end of the central pentagonal (Jisc, and
opposite an interradius, or point of meeting of two rays,
notice a white, circular, raised tubercle, the madreporic
body. When examined with a lens its surface is seen to
be marked by fine undulating radiating lines, which give
to it the appearance of a piece of madrepore coral.

3. The ray which joins the disc on the side opposite the
madreporic body is the anterior ray.

58 HANDBOOK OF IN VKKTKMUATE ZOOLOGY.

4. The two rays between the bases of which the madre-
poric body is placed form the bivium.

5. The anterior ray, together with one on each side of
it, make up the trivium.

6. Notice that, while a line drawn through the anterior
ray and prolonged across the disc would pass through the
madrepbric body and divide the animal into symmetric:! I
halves, this would not be true of a line through any other
ray.

7. Make a sketch, showing these points.

g, Examine a portion of the ab-oral surface with a lens,
and notice the pedicellarim ; small stony pincer-like struc-
tures, which are scattered over the spaces between the
ossicles, and are also found around the bases of the spines.
Each pedicellaria consists of a short stem and a pair of
movable jaws.

h. With a sharp knife cut off one of the rays near its
union with the disc, and examining the cut surface, no-
tice : —

1. The ambulacral ossicles; two long slender plates
which occupy the centre of the oral surface, and form the
roof of the ambulacral furrow. Their lower ends are
widely separated, but the plates incline towards each
other, and their upper, slightly enlarged ends, meet upon
the median line of the ray, above the ambulacral furrow.

2. The upper part of the ambulacral furrow is separated
from the lower open portion by a horizontal membrane-
ous partition, which may usually be found in a dried
specimen, running across from one ambulacral ossicle to
the other just below the point where they meet. The part
thus shut off contains the radiating ambulacral, or water-
tube.

4. From the lower end of each ambulacral ossicle a

STRUCTURE OF THE STARFISH. 59

horizontal plate, the inter-ambulacral ossicle, runs out-
wards and downwards, and forms part of the outer skele-
ton of the ray. On the lower or outer surface of each
inter-ambulacral ossicle two slender spines are articulated
by movable joints at their bases.

4. Running outwards and upwards from the outer ends
of the inter-ambulacral ossicles are much larger and thicker
plates, each of which carries three or four thick club-
shaped movable spines. Each of these plates articulates
with several (three or four) of the inter-ambulacral-
plates.

5. The remainder of the wTall of the ray is made up of
a membrane which contains an irregular network of ossi-
cles with immovable spines.

«'. Make a sketch of the section, showing all these
points.

j. Cut off the ab-oral wall of the ray which has been
removed, and clean off the dried remains of the soft parts,
in order to expose the inner surfaces of the ambulacral
plates. The cleaning will be more easily done after the
ray has been soaked in warm water long enough to
soften it.

1. Notice the vertebral ridge; a longitudinal elevation
along the middle line of the floor of the ray. The ridge
is formed by the union of the upper ends of the ambu-
lacral ossicle, and a shallow longitudinal furrow or suture
marks the line where those of opposite sides meet. The
vertebral ridge is also marked by hundreds of fine parallel
transverse fissures, the sutures between adjacent ambu-
lacral plates. These fissures give the ridge a resemblance
to the vertebral column of a vertebrate. In a ray which
has been softened in water it will be seen that there is con-
siderable power of motion between the ambulacral plates

60 HANDBOOK OF INVERTEBRATE ZOOLOGY.

on opposite sides of the ray, and a very slight power of
motion between those of the same side.

2. On each side of the ridge is an area marked by two
rows of small round openings, and also by tine parallel
lines continuous with the transverse furrows of the ridge,
and therefore at right angles to the long axis of the ray.
This is the area of the ambulacral ossicles. Comparison
of the surface view with the sectional view shows that
each ossicle is a thin, vertically flattened plate, with its long
axis at right angles to the long axis of the ray. It is
joined by its inner end to the corresponding ossicle of the
other side, and by its flat faces to the plates before and
behind it on the same side. In the description of these
plates the face nearest the base of the ray will be called
the proximal and that nearest the tip the distal ; the end
nearest the middle of the ray the central, and that farthest
from the middle line the peripheral. On each side of each
plate there is a perpendicular groove, and the grooves of
adjacent plates meet so as to surround tubular spaces
which run from the interior of the ray to the lower sur-
face.

The inner ends of these tubes, which are the ambulacral
pores, are seen on each side of the vertebral ridge. At
first sight they seem to be arranged in a double row, but
a more careful examination shows that there is only one
pore between each pair of ambulacral plates, but that they
are alternately central and peripheral, thus forming a
"zigzag" instead of a straight line.

Each plate has one groove on each side, one near the
peripheral end and one near the central end, and the posi-
tion of the grooves alternates in adjacent plates, so that if
the groove on the distal side of one plate is near the peri-
pheral end, the groove on the proximal side of the next

STRUCTURE OF THE STARFISH. 61

plate will be at the same end, and the two will form a
tube. The tube between this second plate and the third
will, on the contrary, lie at the central end. '

3. On the outside of the ambulacral area there is an
area marked by a double row of very minute pores ; the
area of the inter-ambulacral ossicles. These are equal in
number and thickness to the ambulacral ossicles, to the
outer ends of which they are united.

4. Outside the inter-ambulacral plates there is a row of
much larger plates, each of which articulates with three
or four inter-ambulacral plates. They are indefinitely
cross-shaped, and are united by the long arm of the cross
to the inter-ambulacral plates, by the cross-bar to adjacent
plates of the same row, and by the top of the cross to the
irregular plates of the ab-oral surface. More careful ex-
amination .shows each to be made up of three distinct
ossicles. Between the arms of adjacent plates are large,
nearly circular foramina, closed by membrane.

k. Make an enlarged sketch of a small portion of the
floor of a ray, showing all these points.

L Clean and examine the lower or external surface of
the same specimen, removing the spines from part of it in
order to expose the plates, and notice : —

1. The double row of ambulacral ossicles and their
pores.

2. A row of inter-ambulacral ossicles on each side of
the ambulacral area.

3. The double row of slender, movable spines, which
these ossicles carry.

4. The row of three or four series of thick spines on
the cross-shaped plates.

5. Trace this latter row of spines to the tip of the ray,
and notice that it passes around the ambulacral and inter-

62 HANDBOOK OF INVERTEBRATE ZOOLOGY.

ambulacra! plates, and unites with the row on the other
side of the ray, to form a terminal tuft of spines upon the
upper surface of the ray close to the tip.

m. Remove the ab-oral wall from the central disc, and
having cleaned away the soft parts, in order to expose the
inner surface of its floor, notice : —

1. The pentagonal mouth-opening.

2. The five anibulacral areas converging at the mouth
to form the sides of the pentagon.

3. Notice that the alternating arrangement of the am-
bulacral pores gradually disappears at the proximal end of .
the ray, so that the last three pores are arranged almost in
a straight line.

4. The last pair of ambulacra! ossicles are much shorter
and thicker than the others, and their proximal edges form
the slightly convex sides of the mouth-pentagon. The
ambulacral pores of this last pair of ossicles pass directly
through the stony matter of the plates.

5. Notice the five inter-radial partitions which separate
the ambulacral areas of adjacent rays, and are formed by
the union of the inter-ambulacral ossicles of one side of
one ray to those of the opposite side of the adjacent ray.
Each of the inter-radial partitions abuts upon one of the
rounded angles of the mouth-pentagon.

6. On each side of the partition there is a perforation
somewhat larger than the ambulacral pores ; the internal
end of the reproductive orifice. Pass a bristle into this
tube, and try to find the external opening on the outer sur-
face of the specimen.

n. Make a sketch of the inner surface of the floor of
the disc.

o. On the lower external surface of the disc, notice that
the rows of inter-ambulacral spines approach each other

STRUCTURE OF THE STARFISH. 63

and unite, and project over the mouth, to form the mouth-
papilla.

1. Carefully remove these spines, so as to expose the
inter-ambulacral plates, and notice that these approach and
unite to form the inter-radial partitions.

p. Make a sketch of the lower surface of the disc.

X. THE STRUCTURE OF THE STARFISH.

( Aster acantheon berylinus.)
INTERNAL ANATOMY.

I. IN an alcoholic or a living specimen notice the fol-
lowing external organs : —

a. The two double rows of tubular feet, or ambulacra,
which project from the ambulacral furrows, upon the oral
surface of each ray.

b. The membraneous peristome which fills the space
between the mouth and the bases of the rays.

c. The nearly circular mouth. In many specimens a
part of the convoluted stomach may be found to project out
of the mouth.

d. The ab-oral tentacles: delicate tubular structures
which project from the ab-oral wall of the body, among
the spines.

II. Study the manner in which the living animal moves
by the use of the ambulacra.

III. The Digestive Organs.

Cut off the tip of one of the rays of the trivium, and
notice the cut ends of the hepatic coecw: two brown sac-
culated organs which are attached by a mesenteric mem-
brane to the inner surface of the ab-or:il Avail of the ray.
There is one on each side of the median line, and they

64 HANDBOOK OF INVERTEBRATE ZOOLOGY.

hang down into the cavity of the ray, which they nearly
fill.

With a knife or a pair of strong scissors cut through the
body wall for about an inch on each side of the ray, just
outside the inter-ambulacral ossicles, taking pains to avoid
injuring the soft parts. Lift up the ab-oral wall by its free
end, and carefully cut the mesenteric membranes which
bind the hepatic coeca to its inner surface. Repeat the
cuts in the same way until the roof of the ray lias been
freed from tip nearly to base. Free the wall of the adja-
cent ray of the trivium in the same way. Lift up the
roof of the disc, and free it from its attachment to the soft
parts, nearly as far as the centre. Cut off and remove
the integument which has been loosened, thus exposing
the internal organs of the two rays and disc. Place the
specimen in a shallow, flat-bottomed dish, cover it with
water, or water and alcohol, and notice : —

a. The large brown sacculated hepatic coeca (Fig.
30, b) ; two in each ray, reaching from the base nearly
to the tip. The dilations of the coeca are arranged in
pairs, and they hang down into the cavity of the ray.

b. Near the base of the ray the sacculations disappear ;
the coeca suddenly constrict, and give rise to a pair of deli-
cate membraneous tubes (Fig. 30, «), which are attached,
like the coeca, to the inner surface of the body-wall, by
mesenteric membranes.

The two tubes soon unite to form a common duct, which
can be traced into the disc.

c. The proximal ends of these ducts open into a large
pentagonal membraneous pouch, the pyloric sac of the
stomach, which fills nearly the whole of the ab-oral portion
cf the, cavity of the disc, and which is attached to the
oody-wall along its edges by mesenteric folds. The angles

STRUCTURE OF THE STARFISH. 65

of the pentagon are opposite the axes of the rays, and the
hepatic ducts open into the ab-oral surface of the sac, a
little above the angles.

d. Near the centre of the ab-oral surface of the pyloric
sac, notice the short, cone-shaped intestine. The anus is
so small that it is very difficult to find. It is a little to
the left of an imaginary line drawn from the uiadreporic
body to the tip of the anterior ray. A line drawn from
the centre of the disc to the angle between the left ray of
the bivium and the left ray of the trivium passes through
the anus.

e. At or near its union with the pyloric sac the intestine
is joined, upon its left side, by a small duct which leads to
a light-colored arborescent pouch ; the respiratory tree
(Fig. 30, </). This pouch is divided into two sacculi,
and these again into small ampullae. Each of the primary
divisions of the organ lies opposite an inter-radius, or
angle (Fig. 30, d) between two rays. One is opposite
the inter-radius between the left ray of the trivium and the
left ray of the bivium, and the other betweeen the left ray
of the trivium and the anterior ray.

f. Radiating from near the centre of the disc are the
five extensor muscles (Fig. 30, n) of the rays. Normally
these are attached to the ab-oral integument. They run
from near the centre of the disc to the tip of each ray,
giving oft', on each side, lateral fibres which are attached
to the ab-oral ossicles. By the contraction of these
muscles the free ends of the rays may be bent upwards
or from side to side.

g. Cut along the sides of one of the unopened rays from
base to tip, and also cut through the ab-oral surface of the
disc at the base of the ray, and through the hepatic duct,
so that the integument, with the organs attached to it, can
be turned out from tne centre ; notice : —

HANDBOOK OF INVERTEBRATE ZOOLOGY.

FIG. 3d

STRUCTURE OF THE STARFISH. 67

FIG. 30. — Starfish opened from above to show the general anatomy.
Drawn from nature by Mr. J. E. Armstrong under the author's direc-
tion.

A. The anterior ray, with the integument of the ab-oral surface
removed, to show the internal organs in place.

B. The right ray of the trivium, with the hepatic coeca turned out,
to show the ambulacral vesicles.

C. The left ray of the trivium, with the ab-oral integument turned
back from the base towards the tip, to show the manner in which the
hepatic coeca are attached to its inner surface.

D. The left ray of the biviuin, unopened.

E. The right ray of the biviuin.

a. Duct from hepatic coeca to stomach, b. Hepatic coeca. c. Madre-
poric body. tl. Inter-radial partition, i. Reproductive organs. (These
were very small in the specimen which was drawn, as it had recently laid
its eggs. Just before*the breeding season, they are very large and extend
nearly to the tips of the rays. )

/. Cardiac pouch of stomach, g. Respiratory tree. h. Retractor
muscles of cardiac pouch of stomach, e. Integument, j. Ampullae.
k. Vertebral ridge. /. Ambulacral plates, m. Inter-ambulacral plates.
n. Extensor muscles of rays.

1. The manner in which the hepatic coeca are attached
to the integument, by mesenteries.

2. The extensor muscle, running along the median line,
between the coeca.

// . Remove the coeca from the adjacent rays by cutting
their ducts, close to the pyloric sac. Under each angle of
the latter, and therefore opposite the axis of each ray, the
stomach will now be seen to project towards or into the
cavity of the ray, thus forming a deeply-folded cardiac
pouch (Fig. 30,/).

The five cardiac pouches, together with the central tube
into which they open, make up the eversable portion of
the digestive tract. An alcoholic specimen may occasion-
ally be found in which these portions of the digestive
tract protrude from the mouth ; and a living specimen
may sometimes be captured with its stomach wrapped

68 HANDBOOK OF INVERTEBRATE ZOOLOGY.

around the shell of a mollusc too large to be taken into
the mouth. After eversion these pouches are drawn back
into the body by five sets of stomach retractor muscles
(Fig. 30, h). These run out for a short distance into
each ray, and are attached to the sides of the vertebral
ridge.

i. 'Cut the muscular attachments of one of the pouches,
and raising it up, notice : —

1. The oesophagus, a short, cylindrical, longitudinally
plicated tube.

2. The peristome, or membrane between the outer end
of the oesophagus and the edge of the mouth-pentagon.

j. Make a sketch to show as many of these points as
possible, and indicate the relation between the various
regions of the digestive tract, and the axis of the rays.

k. Make also a diagram of a side view of the digestive
organs.

I. Open the pyloric sac of the intestine and notice
the valvular folds which guard the opening of the intes-
tine.

IV. The Reproductive Organs.

Remove the digestive organs by cutting the retractor
muscles and the oesophagus. Notice the inter-radial septa
(Fig. 30, d) formed by the union of the inter-ambulacra 1
plates of adjacent rays. Notice the membraneous folds
which form the inner or free edges of these partitions.
In the proximal end of the cavity of each ray, between
the vertebral ridge and the inter-radial partitions are the
light-colored reproductive organs (Fig. 30, i).

There are two of these organs in cadi rav. and their

• «/ '

ducts may be traced into the sides of the inter-radial par-
titions.

V. The Ambulacral or Water Vascular System.

STRUCTURE OF THE STARFISH. 69

The various organs which compose this system are now
exposed. They are : —

a. The madreporic body (Fig. 30, c) ; situated upon
the ab-oral surface of the inter-radius of the bivium.

b. The stone canal (Fig. 31, c) ; a calcareous tube
which passes along the free central edge of the inter-radial
partition from the stonejjanal to a point upon the oral
surface within the mouth-pentagon. The course of the
canal is like the letter S.

c. The ambulacra! vesicles, or ampullae (Fig. 30, j") ;
a double row of small white globular vesicles, with mus-
cular walls, on the inner surface of the ambulacral area, on
each side of the vertebral ridge. The lower side of each
vesicle gives rise to a tube which passes into one of the
ambulacral pores, between the ambulacral ossicles.

d. The Polian vesicles; ten muscular sacculi, some-
what larger than the ordinary ambulacral vesicles, and
situated upon the ton ambulacral plates which form the
sides of the mouth-pentagon.

e. The ambulacra, or feet, which are arranged on the
lower surface in four rows in the ambulacral furrow, along
the oral surface of each ray. If one of the ambulacra
be pulled off and carefully examined, its upper end will
be found to be prolonged to form a small tube which
passes through one of the ambulacral pores to connect
with an ambulacral vesicle.

f. Pull off the feet from a portion of one of the rays
with a pair of fine-pointed forceps, and notice the radial
water-tube, a small longitudinal vessel, which runs along
the middle of the lower surface of each ray at the top of
the ambulacral furrow.

g. Carefully remove the spines which project from the
angles of the mouth-pentagon, and notice the circum-oral

70 HANDBOOK OF INVERTEBRATE ZOOLOGY.

water-tube running around the mouth, just inside the
mouth-pentagon. Trace one of the radiating tubes to the
point of union with the circum-oral tube.

//. Examining the inside of the specimen, notice that
the stone-canal also joins the circum-oral tube.

i. The racemose vesicles; nine small sacculated diver-
tictila, which project inwards from the circum-oral water-
tube opposite all the ambulacral areas except the one
nearest the stone-canal.

j. Make a diagram of the water vascular system.

k. Cut off the top of a ray of a living specimen, and
placing the animal in a tub of fresh sea-water, notice, after
it has recovered from the operation, the manner in Avhich
the ambulacral vesicles inside the ray contract and cause
the protrusion of the corresponding ambulacra, by dis-
tending them with the fluid which is thus forced into
them.

I. Cut off the tip of a ray from a specimen which has
not been opened, and introducing into the radiating water-
tube the point of a small injecting syringe, fill the water
system with a colored fluid, and notice that the ampullae,
the ambulacra, the radiating and circum-oral water-tubes
are all filled. Water which has been colored with a few
drops of carmine dissolved in ammonia may be used in
making the injection ; and if no small injecting-syringe
can be procured, the fluid may be blown into the speci-
men through a glass tube which has been drawn out to a
fine point.

VI. The Nervous System.

Examine the lower or outer surface of the circum-oral
water-tube of an alcoholic specimen with a lens, and notice
a thickened ridge along its outer surface running around
the mouth. This ring is the circum-oral nerve-ring.

STRUCTURE OF THE STARFISH. 71

Kadiating from it are live radial nerves, which lie below
the radiating water-tubes, and which may be traced to the
tips of the rays, where they will be found to end in small
spots of dark-red pigment, the five eye-spots, which are
on the odd ambulacra at the ends of the rays.

VII. Dissect out the stone-canal and notice that it lies in
a membraneous pouch, the pericardium, which is formed
by two folds, along the inner edge of the inter-radial par-
tition. Notice that the lower end of the stone-canal con-
nects with the circum-oral water-tube, while its upper end
joins the inner surface of the madreporic body.

VIII. Notice the Jteart, a membraneous pouch which runs
alongside the stone-canal. In a living specimen the heart
may be seen to pulsate, and when removed and examined
under the microscope it will be found to be made up of a
number of tubular vessels, twisted together. It is very
difficult to trace the course of the blood-vessels, except by
the examination of microscopic sections along their course ;
but they lie in large chambers, the peri-luemal vessels,
and these may be injected, through the pericardium, with
which they communicate, and when filled with coloring
matter, they mark out the course of the true blood-vessels
with sufficient exactness. A fresh specimen should, if
possible, be used in making the injection. With a large
needle drill a hole through the madreporic body, passing
obliquely backwards and downwards from in front, so as
to strike the pericardium on the lower surface of the pos-
terior end of the madreporic body. Introduce a small
canula into the hole, and filling the injecting-syringe
with a colored fluid, such as water colored with carmine
or indigo, force the fluid, very gently, into the peri-
cardium.

If an injecting-syringe cannot be procured, a glass tube,

72 HANDBOOK OF INVERTEBRATE ZOOLOGY.

drawn out to a fine point, may be used to blow in the
fluid.

a C-~

Fiii. 31.

Fio. 31. — Diagram of the water system of a starfish.
(i. Madreporic body. b. Stone-canal, c. Circum-oral water-tube.
d. Radial water-tubes, e. Ampullae. /. Ambulacra.

Tracing the course of the peri-ha?mal tubes by the col-
ored injection, notice : —

a. A circum-oral peri-haemal tube, just below the circu-
lar water-tube, and connecting with the pericardium.

b. Five radiating peri-ha?mal tubes, below the five
radiating water-tubes, and sending branches to the ambu-
lacra.

c. A circum-anal peri-haemal tube, on the inner surface
of the integument of the anal surface of the disc. This
tube, which is pentagonal and much larger than the one
around the mouth, connects with the upper end of the
pericardium, and sends branches to the reproductive
organs, the hepatic coeca, and the stomach.

STRUCTURE OF THE STARFISH. 73

XI. THE MICROSCOPIC STRUCTURE OF THE
STARFISH.

THE smallest specimens which can be procured should
be placed in a quantity of one-half per cent solution
of chromic acid for about twelve hours. They should
then be transferred to a quantity of one per cent chromic
acid, in which they should remain until most of the cal-
careous matter of the skeleton has been dissolved.

With specimens an inch long or less this should be
accomplished in twenty-four hours, but larger specimens
may require several days, and in this case the chromic acid
should be renewed every da}'.

When decalcified the specimens should be placed in
eighty per cent alcohol for twenty-four hours, and they
may then be preserved in ninety per cent or ninety-five
per cent alcohol until they are to be examined.

I. Cut oft* one of the arms, stain and mount it as
directed in Section VII., and cut a number of transverse
sections.

Examining it with a magnifying power of from twenty-
five to fifty diameters, notice : —

a. The remains of the calcareous ossicles (Fig. 32, 6, j?,
and 7) imbedded in the integument. They will probably
retain enough of their calcareous matter to show that they
are formed of a network of calcareous rods or spicules
arranged in rows pretty nearly concentric with the outer
surface.

b. Notice that the spines (Fig. 32, g) of the ab-oral
surface are continuous with the ab-oral ossicles.

1. Around the bases of these spines notice the pedicel-
Iaria3 (f), made up of a shaft and two blades. Notice -

STRUCTURE OF THE STARFISH. 75

FIG. 32. — Diagram of the transverse section of the ray of a star-
fish.

a. The layer of epithelium which invests the outer surface. 6. The
ossicles of the ab-oral surface, c. The layer of epithelium which lines
the perivisceral cavity, d. The layer of epithelium which lines the water
system, e. The epithelial lining of the digestive tract. /. Pedicellariae.
g. Spines of ab-oral surface, h. Ab-oral tentacles, i. Hepatic-coeca.
k. Ambulacral vesicles. I. Radiating water-tube, m. Radiating nerve,
n. The ambulacra, o. Movable spines, carried by the inter-ambulacral
ossicles, p. Inter-ambuiacral ossicles, q. Ambulacral ossicles, r. Me-
senteries, s. Their inner spaces, t. Perivisceral cavity, u. Peri-haemal
spaces.

the joints between these parts, and the muscular fibres
which move them.

c. Notice that the spines (Fig. 32, o) which are carried
by the inter-ambulacral ossicles (p) are furnished with a
movable joint.

if. The ab-oral tentacles (h) which project through the
spaces between the ossicles, and open into, the perivisceral
cavity (t).

e. The layer of epithelial cells, which covers the outer
surface of the body, and which is represented in the dia-
gram by the heavy line a. It covers the pedicellarire and
the spines, and forms the outer surface of the wall of the
ab-oral tentacles.

f. The layer of epithelium which lines the perivisceral
cavity, and which is represented by the shaded line c.
This layer runs into and lines the ab-oral tentacles, and is
reflected out so as to cover all the organs which project
into the perivisceral cavity.

</. Between this layer and the inner surface of the ab-
oral ossicles, a layer of narrow spaces (not sho\vn in the
diagram), lined by another layer of epithelium. In a
transverse section these spares appear as narrow slits.

7^. The cross-sections of the hepatic coeca (i) suspended
to the bodv wall bvthe mesenteries.

76 HANDBOOK OF INVERTEBRATE ZOOLOGY.

1. Notice that the layer of epithelium which forms the
outer surface of the coeca passes down the mesenteries at
r, and is continuous with that which lines the body wall.

2. The coeca are lined by another layer (e).

3. Notice that each mesentery is double, and encloses
a space which is lined by another layer of epithelium.
If a dissected specimen be examined, this space (s) will
be found to open into the peri visceral cavity at the base of
the arm, where the coeca give rise to their ducts. The
lining epithelium is therefore a continuation of the
layer (c).

i. Notice the cross section of the radiating water-
tube (7), in the angle between the two ambulacra!
plates (q).

1. Notice the small tubes which connect this tube with
the ambulacra.

2. Notice the tube which passes through the ambolacral
pore, between the anil mineral plates, and connects the
ambulacral vesicle (A1) with the foot («).

3. The ambulacral vesicle is made up of three
layers : —

(i.) A lining epithelium (d) continuous with the lining
of the water-tube and foot.

(ii.) An outer layer continuous with that which lines
the perivisceral cavity.

(iii.) A layer of muscular fibres between the two.

4. Notice that the foot (n) consists of three similar
layers, but the outer one is continuous with the layer (a)
which invests the outer surface of the ray.

j. Notice that the layer (a) is greatly thickened on the
middle line of the ray under the water-tube, to form the
radiating nerve (m).

k. Between this and the water-tube there is a space (?<)

STRUCTURE OF THE STARFISH. 77

divided into two by a median vertical partition : this space
is the radiating peri-haemal canal.

I. In the partition notice the cut sections of one or two
small tubes, the radial blood-tubes.

m. Notice the muscular fibres which connect the various
ossicles with each other.

1 . Note especially a muscle which runs across the angle
between the ambulacral plates, and separates the water-
tube from the peri-bsemal tube.

n. Cut as thin a section as possible through the organs
in the angle of the ambulacral furrow, and examine it
with a higher power, — one hundred to two hundred and
fifty diameters, — noticing : —

1. The remains of the ambulacral plates (Fig. 33, a m)
arching over the ambulacral furrow.

2. The cross section of the radiating water-tube (r w)
in the angle between the ambulacral plates. If the section
passes through one of the small tubes which run off to the
ambulacra, notice that the layer of epithelium which lines
the large tube also lines the small ones.

3. The muscular band (m) which runs from one ambu-
lacral plate to the opposite one underneath the water*-
tube.

4. Underneath this muscle notice a space (c) divided by
a vertical partition (k) into two. This space is the radial
peri-haemal tube. Notice that the layer of epithelium
which lines it is very thin above and on the partition, but
thickened below, so as to form a pair of opaque granular
pads (I}. As this structure runs along the whole length
of the ray, it is actually not a pad, but a long flattened
band. According to some investigators, it is to be re-
garded as constituting the nerve-fibre of the ray ; and if
this is the true view, it will be seen that there are a pair
of radiating nerve-fibres for each ray.

78 HANDBOOK OF INVERTEBRATE ZOOLOGY.

5. In the partition (k) which divides the peri-haemal
chamber into two, notice the cut ends of two or three
irregular tubes (cZ). These are the true radial blood-
vessels.

FIG. £3.

FIG. 33. — Transverse section of the ambulacra! furrow of the ray of
a starfish, magnified about one hundred arid fifty diameters.

a in. Ambulacral plates. r w. Radiating water-tube. m. Ambu-
lacral muscle, c. Radiating peri-haemal canal, k. Its median vertical
partition. I. Thickened band formed by the epithelium of its floor;
the nerve, according to Lange. d. Radiating blood-vessels. /. Inner
fibrous layer of the surface epithelium; the nerve, according to Lud-
wig. fj. Outer pigmented layer.

STRUCTURE OF THE STARFISH. 79

6. The epithelium of the outer surface (g) of the middle
of the ray is greatly thickened, and is generally regarded
as the true nerve of the ray. It is divided into two sharply
defined layers.

1. An outer layer (g) made up of dark, granular, nu-
cleated cells.

2. An inner layer (f) which consists of: —

(i.) Fibres perpendicular to the outer surface, and con-
tinuous with the granular cells.

(ii.) Very fine longitudinal fibres, which appear as fine
dots in a transverse section (Fig. 33), but as fine parallel
lines in a longitudinal section (Figs. 3^ and 3$7jf). Ac-
cording to Ludwig, the fine longitudinal fibres are the true
nerve-fibres of the ray.

7. Covering the outer surface, notice a very thin, trans-
parent structureless cuticle.

0. Cut a number of vertical sections across the mouth-
pentagon, along the line of an inter-radial partition, and
mounting them, notice : —

1. The cut surface of the inter-ambulacral plate (Fig.
34, i a).

2. The peristome (Fig. 34,^).

3. The epithelium (h) which lines the peri viscera I
cavity (6).

4. The cut sections of the circum-oral water-tube
(c iv).

5. The muscle (m) which connects the ambulacra! ossi-
cles of adjacent rays with each other.

6. The circum-oral peri-hremal vessel, which is divided
into an inner chamber (a) and an outer one (c) by a par-
tition.

7. The circum-oral blood-tube in the partition.

8. The thickened layer of pigmented cells (?) in the

80 . HANDBOOK OF INVERTEBRATE ZOOLOGY.

floor of the outer peri-hsemal channel. This is the circuui-
oral nerve of Lauge.

FIG. 34.

Fio. 34. — Vertical section through the mouth-pentagon in the plane
of an inter-radius, magnified about one hundred and fifty diameters.
(Copied with slight changes from H. Ludwig; Zeit. f. Wiss. Zool. xxx.
Taf. VI.. Fig. 17.)

i a. Iriter-ainbulacral ossicle, m. Muscle which runs between ambu-
lacra! plates of adjacent rays, c tc. Circum-oral water-tube. //. Epithe-
lium of perivisceral cavity. b. Perivisceral cavity. p. Peristome.
a. Inner, and c. outer division of circum-oral peri-ha'inal vessel.
I. Thickened pad formed by the epithelium of the floor of the outer
division of the peri-hannal vessel. /. Fibrous layer of surface epithe-
lium, g. Granular layer of the same.

9. The thickened ridge of surface epithelium (g) which
forms a ring around the mouth between the water-
tube (civ) and the peristome (p). Observe that it is

STRUCTURE OF THE STARFISH.

similar in structure to the thickening in the ambulacra!
furrow.

FIG. 35.

FIG. 35. — Diagram of a vertical longitudinal section through the
mouth pentagon in the axis of a ray, magnified about one hundred and
fifty diameters. (Copied with slight changes from H. Ludwig; Zeit. f.
Wiss. Zool. xxx. Taf. VI., Fig. 16.)

a m. The first ambulacra! plate, a m'. The second ambulacral plate.
c w. Circum-oral water-tube. r w. Radiating water-tube. m and m'.
Muscles which join the pair of plates, o m. m1'. Muscles which join the
pair of plates a m'. a. Inner channel of circum-oral peri-hsemal vessel.
c. Outer channel of same, at the origin of the radiating peri-haemal ves-
sel, d. Radiating blood-vessel, k. The partition which supports it
along the middle line of the ray. e. Partitions which support the lateral
blood-vessels. b,f, y, h, and p. As in Fig. 34.

82 HANDBOOK OF INVERTEBRATE ZOOLOGY.

p. Cut a section through the mouth-pentagon, along the
axis of a ray, and comparing it with the transverse section
of the ray, and with the one through the mouth-pentagon
in the plane of an inter-radius, notice : —

1. The ambulacral plates (Fig. 35, a m, a TO').

2. The peristome (p).

3. The layer of epithelium (h) which lines the perivis-
ceral cavity (A).

4. The radiating wTater-tube (r w) running out from the
circum-oral water-tube (c w).

5. The muscles (m, m', m") which run across the ambu-
lacral furrow, from one ambulacral plate to the other, un-
derneath the water-tube. Notice that while there are two
of these muscles (m and m') for the. first ambulacral
plate (am) there is only one for each of the others. The
fact that the duct which joins the first ambulacral vesicle
to its foot passes through the first ambulacral plate instead
of between it and the second has been already noticed.
This and the presence of two muscles instead of one indi-
cate that this plate really represents two of the series
fused together instead of a single plate.

6. The central channel (a) Of the circum-oral peri-
haemal vessel, in the same position as in the section along
an inter-radius.

7. The partition which separates this from the outer
channel (c).

8. The blood-vessels in this partition.

9. The radiating blood-vessel (d) which runs from this
partition to the tip of the ray.

10. The partition (A1) which runs along the middle of
the ray and supports this vessel between the halves of the
radiating peri-hremal vessel. Notice that the halves of
the radiating peri-haemal vessel communicate with each

HARD PARTS OF THE SEA-URCHIN. 83

other through a wide opening in the top of this partition
under each ambulacral plate.

11. A lateral partition (e) under each ambulacral plate
carries a blood vessel out to the foot and ambulacral
vesicle.

q. Make drawings of the various sections, and trace out
the relation which the parts bear to each other in different
regions of the body.

XII. THE EXAMINATION OF THE HARD PARTS
OF THE SEA-URCHIN.

(Arbacia punctulata.)

SEA-URCHIXS may usually be obtained in abundance at
or a little below low-tide mark in sheltered places among
the fronds of alga?. Either the purple urchin (Arbacia)
or the greenish brown one (Strongylocentrotus) may be
used for laboratory work. The former is more abundant
on the southern coast, while the latter is most easily pro-
cured on the New-England coast.

The following description has been written from speci-
mens of Arbacia, but the differences between the two are
so slight that either form may be used. Specimens should
be preserved dry, and also in alcohol.

I. In a specimen which has been dried without removing
the spines observe the central spheroidal body, flattened
upon one side, and nearly covered by the long, pointed
spines. The flattened surface is the oral or actinal, and a
small area free from spines at the opposite part of the body
is the anal or ab-actinal area. On the oral surface,
notice : —

a. The membraneous peristome, with small irregular

84 HANDBOOK OF INVERTEBRATE /OOLOGY.

calcareous ossicles, forming the wall of the centre of the
flattened oral surface.

1. In the centre of the peristome is the mouth, sur-
rounded by a thickened lip-like fold of the peristoine.

2. The white tips of the five calcareous teeth project
from the mouth, and meet at the centre of the oral surface.

3. Examine the peristome with a hand-lens, and notice
the pedicellarise, each consisting of three movable- jaws
moimtecT upon a long slender movable calcareous stem.

4. Notice five clusters of mushroom-like ambulacra,
or feet, projecting from among the spines around the mar-
gin of the peristome. Each foot is made up of : — :

(i.) A long cylindrical shaft, which during life could be
so lengthened as to reach beyond the tips of the longest
spines.

(ii.) A terminal sucker or flattened disc, which contains
a flat circular calcareous plate.

5. Five pairs of much larger ambulacra project from
the peristome, close to the edge of the mouth.

b. In most dried specimens the ambulacra may be seen
to run in five double lines around the spheroidal body,
like the meridians upon a globe. They lie among the
bases of the spines, and the lines converge towards, but do
not reach, a point directly opposite the mouth.

c. Notice that the whole surface of the body except the
peristome and a small region opposite it, is studded with
long, movable spines.

1 . The spines are arranged in ten sets : five double rows
between the halves of each double row of ambulacra, and
five pyramidal groups between the five double rows.

2. Remove a spine, and after cleaning off the remains
of the muscles by which it was moved, examine it with a
hand-lens, and notice : —

HARD PARTS OF THE SEA-URCHIN. 85

(i.) The long, tapering, longitudinally fluted shaft.

(ii.) The flattened, polished, toothed tip.

(iii.) The ridge or column near the base, which served
for the attachment of muscles.

(iv.) The highly-polished cup, by which each spine
articulates, in a ball and socket joint, with a polished tu-
bercle upon the surface of the shell.

d. The ab-oral area, a small pentagonal region free from
spines, opposite the mouth. The centre of this area is
made up of four flattened, triangular, movable anal plates,
which meet in the centre and form the periproct.

II. Remove the spines and soft parts, and after macerat-
ing the shell for a few days in a strong solution of caustic
potash, examine the hard calcareous corona, which remains
after all the soft parts have been dissolved. Examine first
the ab-oral surface, and notice : —

a. The nearly oval space which, in the fresh specimen,
is occupied by the four anal plates (Fig. 36, a).

b. This space is bounded by the bases of the five trian-
gular ovarian plates (Fig. 36, b). These plates form a
five-rayed star, with a small perforation, the reproductive
opening, at the tip of each ray of the star.

c. One of these plates is a little larger than the other
four ; rough, and covered with minute perforations. The
perforated portion is the madreporic body.

d. A small triangular occular plate (Fig. 36, c) is
wedged into the angle between each two ovarian plates.
Each occular plate is perforated, near its outer edge, by
two very small openings.

(If Strongylocentrotus is used for laboratory work in-
stead of Arbacia, considerable difference will be found in
the arrangement of these plates. The periproct contains a
great number of small plates in place of four large ones.

XO HANDBOOK OF INVERTEBRATE ZOOLOGY.

The madreporic body is very conspicuous and its edges
are sharply defined. The margin of the periproet is formed
by seven plates, the five ovarian and two of the occular
plates, and the perforations through the occular plate are
much larger than they are in Arbacia, and there is only
one in each plate instead of two.)

FIG. 36.

FIG. 36. — The ab-oral surface of the corona of Arbacia punctulata, a
little enlarged. (Drawn from nature by Mr. H. J. Rice, under the author's
direction. )

a. Anal plates. b. Ovarian plates. c. Occular plates, d. Intor-
ambulacral sutures, e. Tubercles on arabulacral plates. /. Ambulacral
sutures, y. Ambulacral pores, h. Tubercles on inter-ambulacral plates.
1, 2, S, 4, 5. The five rays.

HARD PARTS OF THE SEA-URCHIN.

e. Examine the oral surface, and notice : —
1. The large mouth-pentagon which forms nearly the
whole oral surface of the corona, and is normally closed
by the peristome. The aperture is pretty definitely pen-
tagonal ; the angles are concavely rounded, and there is a
deep notch in the middle of each side.

FIG. 37.

Fir,. 37. — The oral surface of the corona of Arbacia, a little enlarged.
(Drawn from nature by Mr. H. J. Rice, under the author's direction.)
The letters and figures of reference are the same as in Fig. 36.

2. The five inter-radial sutures (Figs. 36 and 37, d} : zig-
zag lines which run around the corona from the tip of each

88 HANDBOOK OF INVERTEBRATE ZOOLOGY.

ovarian plate to the corresponding angle of the mouth-
pentagon. These sutures divide the corona into five areas
or rays (Figs. 36 and 37, 1, 2, 3, 4, 5), the broad ends
of which abut upon the mouth-pentagon and form its
sides, as in the starfish, while the tip of each ray lies be-
tween two of the ovarian plates, and ends with an occular
plate.

/. Mark three of the inter-radial sutures with ink, and
notice a second time the points mentioned in e.

g. Observe the double row of convex, highly-polished,
alternating tubercles for the attachment of spines, along
the middle of each ray (Figs. 30 and 37, e, e, e, e). No-
tice that these double rays run from an occular plate to the
notch in the middle of the corresponding side of the mouth-
pentagon.

h. In the middle of each double row a zigzag ambu-
lacral suture (Figs. 36 and 31,f,f,f,f). This line also
runs from an occular plate to the middle of a side of the
mouth-pentagon. It corresponds to the suture along the
vertebral ridge of a starfish, and is formed by the meet-
ing of the two sets of ambulacral ossicles which constitute
the ambulacral area in the middle of each ray.

i. On each side of the double row of tubercles a double
row of ambulacral pores (Figs. 36 and 37, g, g, g, g).

j. Outside the ambulacral area a row of inter-ambulacra 1
plates (Figs. 36 and 37, A, A, A, A). The outer ends of
the inter-ambulacral plates on opposite sides of adjacent
rays meet to form the inter-radial suture.

k. Break a corona to pieces by pulling upon opposite
edges of the mouth-pentagon. Notice that the plates
separate most readily along the inter-radial sutures.
Break off some of the inter-ambulacra] plates, and notice
that they separate from the ambulacral plates along a

HARD PARTS OF THE SEA-URCHIN. 89

definite, nearly straight suture, just outside the area of
ambulacral pores. Each inter-ambulacral plate is nearly
rectangular, the sides being longer than the ends. It
articulates by its sides with the adjacent inter-ambulacral
plates of the same series ; by one of its ends with the am-
bulacral plates of the same ray ; and by the other end,
which is pointed, with the ends of inter-ambulacral plates
of the adjacent ray. On the outer surface of each inter-
ambulacral plate are from one to four tubercles for the
attachment of spines.

I. Draw a group of inter-ambulacral plates, showing
the manner in which they unite with all the plates which
touch them.

m. Break up a small portion of an ambulacral area,
observing that the plates of the two sides of the ray
separate readily along the ambulacral suture, while those
on the same side of the ray separate from each other much
less readily along sutures which are perpendicular to and
opposite the angles of the ambulacral suture. Notice : —

1. That each plate is similar in shape to an inter-ambu-
lacral plate. They are so placed that their flat ends artic-
ulate with the flat ends of the inter-ambulacral plates, and
their pointed ends with the ambulacral plates of the other
half of the ray.

2. On the outer surface of each plate, near the pointed
end, a tubercle for the attachment of a spine.

3. The opposite end, — the end farthest from the middle
of the ray, — is perforated by three or four pairs of am-
bulacral pores. The two pores which form a pair are
inclined towards each other, so that their external ends
are much closer together than their internal ends. The
one nearest the middle of the ray serves for the pas-
sage of the tube which joins the foot to the radial water-

90 HANDBOOK OF INVERTEBRATE ZOOLOGY.

tube, the latter being inside the shell of the sea-urchin.
The other pore, the one nearest the inter-ami mlacral
suture, is that through which each foot is connected with
its ampulla. The growth of the ambulacral plates shows
that each one of them is compound and really consists of
as many separate plates as there are pairs of ambulacra!
pores. With care the lines between these smaller plates
may be made out, as shown in Fig. 38, and they remain
distinct through life around the mouth-penta-
gon, as shown in Fig. 37.

FIG. 38. — Five ambulacral plates from the point
marked "A," in Fig. 36, more enlarged, to show the
S«M ondary plates of which they are made up. (Drawn
FIG. 38. from nature by Mr. H. J. Rice.)

7i. Make a sketch of a few ambulacral plates, showing
as many of these points as possible.

o. Notice that each occular plate is at the end of a series
of ambulacral plates, as in the starfish, while the ovarian
plates, like the reproductive orifices of the starfish are oppo-
site the inter-ambulacral sutures.

p. Make a sketch of the alvoral surface of the corona,
showing all the plates and sutures : and indicate in the
sketch the limits of the five rays.

q. Make a similar sketch of the oral surface.

r. Notice the five pairs of auriculae, or perpendicular
plates, which project upwards from the inner surfaces of
the ambulacral plates which form the sides of the mouth-
pentagon.

INTERNAL STRUCTURE OF THE SEA-URCHIN. 91

THE INTERNAL STRUCTURE OF THE SKA-
URCHIN.

(Arbacia Punctulata.)

CAREFULLY remove the spines from an alcoholic or a fresh
specimen ; place it, mouth uppermost, in a shallow pan
or a bowl, and pour on enough dilute acid to cover all but
the oral surface (two per cent, nitric acid will answer).
After it has remained in the acid long enough to remove
the calcareous matter from the integument, — from
twenty-four to forty-eight hours, — wash it thoroughly
with water. Place it in a shallow pan. with enough
water, or water and alcohol, to cover it, and cut, with a
pair of sharp-pointed scissors, through the integument
just outside of and entirely around the periproct, taking
care to cut no deeper 'than the integument. From the
edges of this circular incision make five radiating cuts
along the lines of the inter-ambulacral sutures down to
the oral surface.

I. Turn back the five flaps, and notice the following
structures : —

a. The five large sacculated reproductive glands (Fig.
39, a), reddish-brown in the female, and gray in the male.
They occupy the upper ends of the inter-ambulacral areas,
and are attached to the integument in such a way that
each would be split into halves if the five radiating in-
cisions were deep enough.

b. On the middle line of the inner surface of each flap
notice the radial water tube (Fig. 40, i).

c. On each side of this a single row of flattened, leaf-
like ampulla? (Fig. 40,/).

HANDBOOK OF INVERTEBRATE ZOOLOGY.

d. Turn the periproct over, and notice : —

1. The five genital ducts, which run from the reproduc-
tive organs to pass through the pores of the ovarian plates
to open on the upper surface.

2. The dark brown intestine (Fig. 39, tZ), opening in
the centre of the periproct.

Fio. 39.

FIG. 39. — Side view of Arbacia ptmetulata, with the spines and part
of the corona removed, to show the internal organs. (Drawn from nature
by H. J. Rice, under the author's direction.) A little enlarged.

a. Reproductive organs. d. Intestine. e. (Esophagus. /. Pyloric
division of stomach, g. Cardiac division of intestine.

3. The oesophagus, e; a somewhat similar brown tube,
which forms a loop close to the anal end of the intestine.

4. From this loop the oesophagus passes into the centre
of the upper surface of a large complicated structure,

INTERNAL STRUCTURE OF THE SEA-URCHIN.

Aristotle's lantern, which is made up of a great number
of calcareous plates, and projects from the peristome into
the body cavity.

5. In contact with the wall of the oesophagus, a small
membraneous tube, the stone canal (Fig. 40, a) runs from
the madreporic body across the perivisceral cavity to the
lantern.

FIG. -!0.

FIG. 40. — Internal view of the oral half of the corona of Arbacia
punctulata, to show the muscles of the lantern. (Drawn from nature by
H. J. Rice, under the author's direction.)

". Stone canal, b. Circular water tube. c. Concentrator muscles of
lantern. d. Tendons of lantern, e. Protractor muscles. /. Radulae.
</. Radii, h. Retractor muscles, i. Radial water tubes, j. Ampullae.

6. The stone canal joins the circum-oral water tube
(Fig. 40, b), which surrounds the oasophagus where it
enters the lantern.

94 HANDBOOK OF INVERTEBRATE ZOOLOGY.

7. On the side of the upper end of the stone canal
notice a small dark brown corrugated pouch, the heart.

e. Cut the stone canal, and separate the wall of the
intestine from the wall of the oesophagus, and turning the
periproct to one side, trace the course of the digestive
tract, noticing : —

1. The intestine, (Fig. 39, d), running downwards
from the anus, and passing through one of the repro-
ductive organs, underneath which it joins the " pyloric "
chamber of the stomach.

2. This is a long, flat, wrinkled brown tube,y, which
runs around nearly the whole circumference of the body.
Its inner or central edge is free, but its outer edge is
attached to the integument on each side of each ambu-
lacral area. Notice the small, lighter-colored vessel which
runs along its inner or free edge. After running around
the body, it bends down upon itself to join the " cardiac "
chamber (Fig. 39, g).

3. This also runs almost entirely around the body, but
in the opposite direction. Its outer edge is folded or sac-
culated, and is attached by mesenteric membranes to the
integument on each side of each ambulacra! area, while
its inner margin is free, and bounded by a large, smooth-
walled tube, which is sharply distinguished from the outer-
sacculated portion. After encircling the body, the car-
diac chamber bends upwards to join the oesophagus, e.

4. This is a somewhat smaller tube, which makes two
abrupt bends upon itself, and then passes up on to the
ab-oral surface of the lantern to enter the channel in its
centre.

/. Make a drawing, showing as many of these points as
possible.

II. Examination of the dentary apparatus and its

INTERNAL STRUCTURE OF THE SEA-URCHIN.

muscles. The dentary apparatus, or lantern, is now ex-
posed, together with its complicated system of muscles,
occupying the .centre of the oral half of the body cavity.
Before examining the muscles the hard parts should be
studied, and this may be done to best advantage with a
dried specimen. In such a specimen notice : —

a. The points of the five teeth protruding from the
mouth.

b. Cut with a sharp knife through the peristome, close
to the stony edge of the mouth pentagon ; lift up one edge
of the peristome and pull the lantern out of the shell. It
is made up of a number of calcareous pieces, which are
so arranged as to form a cone, with a broad, flat, circular
base (Fig. 41, a), which is turned

towards the anal surface ; and an
oral apex (Fig. 41, b), made up of
the tips of the five teeth. The
axis of the cone is a tube for the
passage of the oesophagus. Pull
off the peristome, and the remains
of any soft parts which may adhere
to the lantern, and in a side view
notice : —

FIG. 41. — Side view of the lantern.
(Drawn from nature by H. J. Rice.)

a. Upper surface of base. b. Apex.
c. Alveoli. d. Teeth. e. Epiphyses.
/. Raduhe.

1. The five triangular pieces or alveoli (Figs. 41 and
42, c), which carry the teeth. The peripheral surface of
each alveolus is nearly an isosceles triangle, with a short
l>as<>, and two much longer sides. The base is at the top,
the acute angles at the bottom, and the long sides of ad-

— C

96 HANDBOOK OF INVERTEBRATE ZOOLOGY.

jacent alveoli are parallel. The acute angle is truncated,
and the tip of the tooth completes the triangle. The base
is not a straight line, but a deep, re-entrant angle, which
reaches nearly half way to the vertex.

(i.) Along the middle line of the alveolus a straight
suture marks the union of the two parts which compose it.

(ii.) Opposite the vertex of the re-entrant angle the
inner end of the tooth (d) may be seen.

(iii.) The upper or basal angles of the cluster are pro-
longed to form a pair of horn-like processes (e), which
lean towards each other and towards the axis. They are
immovably joined to the alveoli, although they are in reality
distinct pieces, or epiphytes, separated from the alveoli
by sutures.

2. The dried, dark-colored remains of the concen-
trator muscles, which bind the parallel faces of adjacent
alveoli to each other.

3. Over the points where the basal angles of the five
alveoli approach each other, notice the flattened, periphe-
ral ends of five plates, the radii (Figs. 40, f, and 41, <?),
which lie on the flat inner end of the lantern.

4. Under the ends of the five radii notice the outer ends
of the five radula? (Fig. 40, </), each of which articulates,
by a movable joint, to the basal angles of two alveoli.

5. Make a drawing of a side view of the lantern, show-
ing all these points.

6. On the inner or flat surface of the lantern notice : —
(i.) The axial tube for the passage of the oesophagus,
(ii.) The five radulre, rectangular in a surface view, and

with their central ends meeting around the oesophagus.
Notice at the outer end of each radula the notches by
which it articulates with the alveoli.

(iii.) The five radii running along the middle lines of the

INTERNAL STRUCTURE OF THE SEA-URCHIN. 97

radulse, and articulating with them centrally, while their
peripheral ends are free.

(iv.) The ten epiphyses, articulating with the ends of the
radulse.

(v.) The free inner ends of the five teeth.

7. Make a drawing showing all these points.

8. Remove one of the alveoli, and in a side view
notice : —

(i.). The flat surfaces (Fig. 42, b] by which adjacent
alveoli face each other.

(ii.) The parallel horizontal ridges for the
attachment of the concentrator muscles.

(iii.) The groove or joint along the upper
edge, for articulation with the radulae.

FIG. 42. — Side view of an alveolus. (Drawn from na-
ture by H. J. Rice. )

6. Flat surface of alveolus, c. Outer surface, d. Tooth.

(iv.) The open space between the central edges of the
halves of the alveolus.

(v.) The long tooth (Fig. 42, d) set into the socket
formed by the alveolus. Take out the tooth and notice : —

(a.) The exposed pointed cutting edge.

(5.) The ridge or keel along the inner surface.

(c.) The long, imbedded, growing portion of the tooth.

c. The muscles of the lantern may now be examined in
an alcoholic specimen. Notice : —

1. The five transverse muscles (Fig. 40, c) which con-
nect the five radii with each other on the inner surface of
the lantern.

2. A pair of tendons (Fig. 40, d) running outwards
and downwards from the outer end of each radius to the
inter-ambulacral areas of the inside of the shell.

98 HANDBOOK OF INVERTEBRATE ZOOLOGY.

3. Between each p«air of these a pair of protractor
muscles (Fig. 40, e) running from the upper angles of
each alveolus to the corresponding inter-ambulacral area.

4. Five pairs of retractor muscles (Fig. 40, />) running
from the auriculae to the oral ends of the alveoli.

' 5. The inter-alveolar muscles, running between the
faces of adjacent alveoli.

6. Make a sketch of the lantern, with its muscles.

d. Notice the radiating water tu'bes (Fig. 40, /) which
pass out from under the outer ends of the raduliu ; run
down over the outer surfaces of the inter-alveolar muscles,
and then pass out between the auriculae, and run upwards
along the inter-ambulacral suture to the ovarian plate.
Notice the flat, leaf-like ampullae upon each side of the
water tube.

e. The nervous system. As the nerve ring is situated
upon the inner surface of the peristome, between the
oesophagus and the tips of the alveoli, it is necessary to
carefully cut away one side of the lantern, in order to
expose it. This may be done by breaking the alveoli
away in small pieces, with a pair of strong scissors. After
exposing the nervous system, notice : —

1. The circum-oral nerve ring, a pentagonal ridge
around the oesophagus, just inside the tips of the five
teeth.

2. The five radiating nerve fibres running along the
ambulacra] sutures from the angles of the pentagon to the
ovarian plates outside the water tubes, or between them
and the corona.

EMBRYOLOGY OF ECHINODERMS. 99

XIV. THE EMBRYOLOGY AND METAMORPHOSIS
OF ECHINODERMS.

THE eggs of the Echinoderms are especially adapted
for examination by a beginner, on account of the sim-
plicity of the early stages ; and the student of the elements
of morphology can nowhere find more favorable material
for studying the more general features of embryology.
The eggs of Arbacia are in certain respects unfavorable
for the study of the special features of echinoderm embry-
ology, but the ease with which they may be procured and
reared, and the fact that the breeding season extends
through the whole summer, render it, on the whole, the
best form for our purpose.

Those who wish to pay more extended attention to the
subject may study the eggs of Strongylocentrotus, in con-
nection with those of Arbacia ; for while the opacity of
the latter renders the observation of their internal struc-
ture very difficult, the eggs of Strongylocentrotus are
transparent. The excellent figures, by Alexander Agas-
siz, of the metamorphosis of Strongylocentrotus, have
been reproduced in Agassiz' Seaside Studies, Packard's
Life Histories, Balfour's Comparative Embryology, and
other text-books ; so that the student can readily obtain
from them such guidance as he will need for more ex-
tended research.

I. The fertilization of the eggs of Arbacia. The
spawning season of this species on the southern coast ex-
tends from early spring to the end of August, and on the
northern coast it probably lasts several weeks longer.

The eggs may be obtained by chopping up the ovaries ;
or they may usually be obtained after they have been laid.

100 HANDBOOK OF INVERTEBRATE ZOOLOGY.

In order to obtain them and fertilize them artificially,
open a number of fresh specimens by cutting across the
middle of the shell horizontally with a strong knife.
Notice that the reproductive organs of some of them, the
females, are dark brown, while those of others, the males,
are milky white. After two or three of each sex have
been opened, cut out a small fragment of the ovary of a
female, and place it on a glass slide, with a drop of watt T,
and pressing and moving it gently, notice that the minute
brown eggs escape into the water. After these have been
shaken out of the fragment throw it away, and examine
the drop under the microscope with a power of fifty to
one hundred diameters, noticing the dark, brownish-red,
spherical yolks, with their thick, transparent shells. If
the eggs are of uniform size and color, they are probably
ripe, and ready for fertilization ; but if they vary much
in size, and if some are more transparent than others,
other specimens should be examined until one is found in
which the eggs are more uniform. Place this specimen
on one side, where it can be recognized, and keep it until
a ripe male is found.

Cut a small fragment from the white testis of a male,
and tear it to pieces in a drop of water, and examine, with
a power of about one hundred diameters, the white fluid
which escapes. It will be found to consist, in great
part, of minute granules, which can barely be recognized
with this power. These particles, which are the sperma-
tozoa, will be seen to be in constant dancing or jerking
motion. It is rather difficult for a beginner to determine
whether the spermatozoa are fully ripe or not. The best
plan is to examine fluid from several males, and to set
aside the one in which they are most uniform in size and
active in motion.

EMBRYOLOGY OF ECHINODERMS. 101

Place a drop of fluid from the testis of this male upon a
clean slide, cover it with a cover glass, and examining it
with a power of two hundred and fifty to five hundred
diameters, notice that each spermatozoon consists of a
small, highly refractive, rounded "head," and a long,
slender, undulating "tail, "and is somewhat tadpole-shaped.
If, with this power, the spermatozoa appear uniform in
size, and if there is little or no fine granular matter scat-
tered among them, the fluid is probably ripe.

Carefully cut out the reproductive organs of the male
which has been selected, and placing them in a large
watch-crystal, chop them up with a pair of scissors, to
facilitate the escape of the spermatozoa. Pick out and
throw away the fragments, and pour or wash the milky
fluid into a small tumbler or beaker, with about half a
pint of fresh sea-water.

Set this aside, and chop up in the same way the ovaries
of the female which has been selected. Pick out the
fragments, and pour the red fluid into the water which
contains the spermatozoa, and having gently stirred it for
a minute or two, set it aside to allow the eggs to settle to
the- bottom.

In about half an hour, carefully pour or siphon off the
water, replace it with fresh, and stir for a minute or two.
Repeat this process at the end of. another half hour,
and so on until the water, after the eggs have settled, is
clear and transparent. Set it aside where it may have
plenty of light, without exposure to the sun. In about
twenty-four hours, the larvse which have hatched will be
found swimming close to the surface of the water. Care-
fully .siphon them off, or draw them up with a dipping-
tube, and place them in another tumbler of water, in
order that they may not be poisoned by the decomposition

102 HANDBOOK OF INVERTEBRATE ZOOLOGY.

of those eggs which do not hatch. In about twenty-four
hours more, place them in a larger tumbler, and till this
up with fresh sea-water, and repeat this every day. After
five or six days, it will be best to distribute the lame
among several small tumblers of water, by picking up a
few with a dipping-tube, and placing them in each tum-
bler. As they grow larger, they may be picked out and
placed in a watch-crystal every day while the water is
changed.

If specimens can be found in the act of discharging
their reproductive elements, there will be no need of dis-
section. If a number of specimens are placed for a few
hours in a large tub of sea-water, some of them may dis-
charge the brown ova and white male fluid from the ori-
fices in the reproductive ossicles. As these reproductive
elements settle to the bottom, they may lie drawn up
through a long dipping -tube, and
mixed as above described.

II. Microscopic examination of the
segmenting egg.

FIG. 43. — A newly-laid egg of Arbacia punc-
tulata, magnified about two hundred diameters.
(From a sketch by II. Garman. )

a. Eggshell, b. Yolk. c. Germinative vesicle.

a. The unfertilized egg. When this is examined with
the microscope, it is seen to be perfectly spherical (Fig. 43),
consisting of an opaque, brownish-red yolk (/>), sur-
rounded by a thick, transparent shell (a). When crushed
under a cover glass, the yolk will be found to owe its color
to minute reddish granules, or food particles, which till
the transparent protoplasm so completely as to color it
uniformly. Near the surface of the yolk, notice a round,

EMBRYOLOGY OF ECHINODEKMS.

103

transparent spot, the germinative vesicle (c) ; rather diffi-
cult to detect in the opaque egg of Arbacia, but more dis-
tinct in the egg of Strongylocentrotus.

b. A few minutes after the egg has been placed in the
male fluid, its surface will be found to be thickly covered
with spermatozoa, which are attached to it by their
" heads," while their " tails " continue in motion with such
activity that they may cause the egg to spin or roll
through the water. At about the same time the germina-
tive vesicle ceases to be visible, although the examination
of the more transparent eggs of Strongylocentrotus shows
that it does not actually disappear, but undergoes impor-
tant changes. As these cannot be ob- a:
served in our species, however, they will
not be described here.

FIG. 44. — Egg of Arbacia punctulata, a few
minutes after fertilization. (From a sketch by
H. Gannan. )

d. Principal axis. e. Furrow indicating the
position of the first cleavage plane. FIG. 44.

Soon after the germinative vesicle becomes invisible,
the yolk (Fig. 44) becomes slightly notched at a point e,
upon its periphery, and it is therefore
no longer spherical, but divisible into
symmetrical halves in the plane (d), of
Fig. 44. The axis which lies in this
plane is now different from any other

FIG. 45. — Egg at the end of the first period of
active segmentation. (From a sketch by H. Gar-
man.)

/. Direction cell. d. Principal axis.

which can be drawn through the centre of the egg, and
is known as the principal axis. In a few minutes more,

104

HANDBOOK OF INVERTEBRATE ZOOLOGY.

the notch (e), is much deeper, and a small, transparent
body, the "direction-cell" (Fig. 45, /), separates from
the yolk in the notch. The direction cell takes no part
in the development of the embryo, and soon disappears
in Arbacia, although, in other animals, it may persist for
some time, thus indicating in the embryo the point occu-
pied by the principal axis. That end of the principal axis
where the direction cell is situated is known as the germi-
native pole, while the opposite end is known as the nutri-
tive pole.

The notch deepens rapidly ; soon runs entirely through
the egg, and divides it, along the principal axis, into two
equal and similar masses, the two primary segmentation
spherules (Fig. 45) . At the same time, a circular, slightly
transparent spot, the segmentation nu-
cleus, becomes indistinctly visible in
each spherule.

FIG. 46. — Egg during the period of rest which
follows the first period of segmentation. (From a
sketch by H. Gannan. )
FIG. 46.

c. The first division of the egg goes on quite rapidly,
but as soon as it is completed, the egg passes into a rest-
ing stage ; the two spherules flatten against each other,
the fissure between them becomes in-
distinct, as shown in Fig. 46, and the

for some time without

change.

FIG. 47. —Egg at the beginning of the second
period of segmenting activity.

g. fj. Beginning of the second cleavage furrow.

FIG. 47.

d. The next period of activity is initiated by the reap-

EMBRYOLOGY OF ECHINODERMS.

105

pearance of the distinct furrow between the two spherules.
The segmentation nuclei then become invisible (Fig. 47),
and traces of a second division make their appearance at
right angles to the first, but, like the first, in the plane of
the principal axis. Four segmentation nuclei now appear
in place of the two, and the egg soon becomes divided
into four spherules, as shown in Figs. 48 and 49. The
first of these figures gives a polar view, or a view in the
line of the principal axis, while the second is a side view,
or one at right angles to this axis.

FIG. 4s.

FIG. 49.

FIG. 50.

FIG. 48. — Egg at the end of the second period of activity, viewed
from one end of the principal axis. ( From a sketch by H. Garman. )

FIG. 49. — The same egg viewed at right angles to the principal axis.
(From a sketch by H. Garman. )

FIG. 50. — An egg during the resting stage which follows the second
period of activity, seen from one of the poles of the principal axis.
(From a sketch by H. Garman.)

e. The five spherules now flatten against each other, the
line between them becomes indistinct, and the egg passes
into the resting stage (Fig. 50).

f. The spherules again become distinct, and a plane of
division makes its appearance at right angles to the prin-
cipal axis, and soon divides each of the four into two, so
that the egg now consists of eight (Fig. 51).

(j. This division is followed by a resting stage, shown
in Fig. 52.

106 HANDBOOK OF INVERTEBRATE ZOOLOGY.

h. During the next stage of activity, each of these
eight becomes divided into two, by a cleavage along a
plane passing through the principal axis. In a polar
view (Fig. 54), eight of the sixteen spherules thus formed
are visible, while ten are visible in a side view (Fig. 55).

FIG. 51. FIG. 52. FIG. 53.

FIG. 51. — Side view of an egg at the end of the next period of ac-
tivity. (From a sketch by H. Carman.)

FIG. 52. — Similar view of the same* egg during the next period of
rest. ( From a sketch by H. Garman. )

FIG. 53. — View of one of the poles of the principal axis of an egg,
at the commencement of the next period of activity. (From a sketch by
Mr. H. Garinan.)

FIG. 54. FIG. 56. FIG. 56.

FIG. 54. — Similar view of the same egg at the end of the period of
activity. (From a sketch by Mr. H. Garman.)

FIG. 55. — Side view of the same egg. (From a sketch by Mr. H.
Garman.)

FIG. 56. — Surface view of an egg in an advanced stage of segmenta-
tion. (From a sketch by Mr. H. Garman. )

i. Repeated divisions increase the number and diminish
the size of the spherules, and in from three to twenty-four

EMBRYOLOGY OF ECHINODEKMS.

107

hours, according to the temperature, the eggs present the
appearance shown in Fig. 56. Careful examination, in a
good light, will now show that the egg is hollow, and
consists of a spherical shell (Fig. 57, A), around a central
space, or segmentation cavity, i. The shell consists of a
single layer of wedge-shaped spherules or cells, each of
which contains a nucleus.

FIG. 57. FIG. 58.

FIG. 57. — Diagram of the same egg, seen in section.

h. The single spherical layer of cells, i. The segmentation cavity.

FIG. 58. — Diagram of the embryo as seen in section at the beginning
of the gastrula stage.

i. Segmentation cavity, j. Ectoderm, k. Endoderm. m. Orifice of
invagination.

III. The Gastrula stage. One side of this shell now
becomes invaginated, or pushed in towards the other, as
shown in Fig. 58, thus forming a second cavity, m, the
primative digestive cavity, which opens externally by a
large, funnel-shaped orifice, the gastrula mouth, or orifice
of invagination. As the direction cell does not persist in
Arbacia, the relation between the principal axis and the
ingrowth cannot here be made out, but the analogy of
other animals gives great reason to believe that the invagi-
nation takes place along the principal axis, but at the
nutritive pole or opposite the direction cell. The layer of
cells is now divisible into two portions : the endoderm (&),

108 HANDBOOK OF INVERTEBRATE ZOOLOGY.

which has been developed from the cells formed at the
nutritive pole, and pushed inwards to form the lining wall
of the digestive cavity, and the ectoderm, which is formed
from the formative pole of the egg, and is to give rise to
the outer wall of the body. The segmentation cavity (z),
is no longer spherical, since the ingrowth of the digestive
cavity encroaches upon it. The opacity of the egg of
Arbacia prevents accurate study of its internal structure,
but in Strongylocentrotus careful examination with high
powers will show that the inner ends of the endodcrm
cells are separating off and forming stellate amoeba-like
cells, which are free in the segmentation cavity. These
are the mesoderm cells, which after a time become ar-
ranged in a layer around the segmen-
tation cavity on the inner ends of
both ectoderm and endoderm cells.
The outer surface of the body now
becomes covered with fine cilia, and
the embryo escapes from the egg-
shell, and swims at the surface of the
0. \l ^ II water.

Fro. 59. — Side view of the larva shortly after
its escape from the egg. (Drawn from nature
FIG. 59. by W. K. Brooks.)

During the second or third day, the embryo elongates
in a line nearly at right angles to the principal axis, and
at the same time becomes nearly triangular when seen in
side view (Fig. 59). The angles are short and rounded,
and one of them («), is at what may now be called the an-
terior end of the body, another (&), at the posterior end.
and a third near the middle of what will be called the
ventral surface. The longest side (a, b), is nearly straight,

EMBRYOLOGY OF ECHINODERMS.

109

and forms the dorsal surface, while the two short sides,
a, c, and c, b, together make up the ventral surface.

The orifice of invagination (o), is now situated between
the angle (c) , and the posterior end, and the primative di-
gestive cavity is no longer in the centre of the body, but
bends towards the anterior end. Owing to the opacity of
the embryo of Arbacia at this stage, the internal structure
cannot be very clearly made out, but careful examination
will show that the endoderm and the ectoderm of the
anterior end of the body are still quite thick, while the
ectoderm is quite thin at the posterior end. In the more
transparent embryo of Strongylocentrotus at the same
stage, the inner end of the digestive tract may be seen to
be constricted off as a
small sac, the water pouch; &•

and the mesoderm cells
may be made out as an
internal layer of cells, lin-
ing the body cavity on the
inner end of the digestive
tract.

FIG. 60. — Ventral view of
the same larva. (Drawn from
nature by W. K. Brooks. )

a. Oral or anterior end.
6. Posterior end. c. Ciliated
ridge, d. Calcareous spicules.
e. Orifice of invagination.

In a ventral view of the same larva of Arbacia at this
stage (Fig. 60), the angle c, (Fig. 59) which is seen in a
side view, is found to be the profile of an elevated ridge
(Fig. 60, c), which runs across the ventral surface near
the anterior end, and divides the body into a large pos-
terior lobe (6), and a much smaller anterior lobe (a). The

110

HANDBOOK OF INVERTEBRATE ZOOLOGY.

orifice of invagination, or anus (o), is situated just behind
the centre of the ridge, and the cilia on the anterior lobe
and ridge are long, while those on the posterior lobe and
dorsal surface are small. A number of brownish-red pig-
ment spots are scattered over the surface of the body.

At each end of the ridge, which will be spoken of here-
after as the ciliated ridge, there is a small, transparent,
three-pronged spicule (d), the beginning of the calcareous
skeleton of the larvae. By comparing the side view with
the ventral view, one of the prongs of this spicule will be

seen to point towards
the anterior lobe, one
towards the posterior
lobe, while the third
runs along the ciliated
ridge, towards the mid-
dle of the ventral sur-
face.

IV. The Develop-
ment of the Pluteus or
swimming larva.

FIG. 61. — Ventral view of
an older larva. (Drawn from

nature by W. K. Brooks. )
FIG. 61.

a. In the ventral view of a larva from twelve to eigh-
teen hours older (Fig. 61), the ciliated ridge is much
more marked, and projects beyond the outline of the
body, so that the sides of the anterior and posterior lobes
are concave. The posterior branch of the spicule, a, is
greatly lengthened, and reaches nearly to the posterior
end of the body, while a fourth branch has made its ap-
pearance, and runs towards the anterior edge of the cil-
iated ridsre.

EMBRYOLOGY OF ECHINODERMS.

Ill

In a side view (Fig. 62), the outline of the body
is much as it was at the last stage, but the ecto-
derm is pushed inwards between
the ciliated ridge (c), and the
anterior lobe («), so as to nearly
meet the digestive tract, thus indi-
cating the point (m), where the
mouth is soon to be formed by the C,
union of the ectoderm of the ante-
rior end of the body to the endo-
derm of the inner end of the prima-
tive digestive cavity.

— i.

-a.

FIG. 63.

FIG. 62. —Side view
0. of the same larva.

FIG. 63.— Ventral
view of an older larva.
(Drawn from nature by
W. K. Brooks.)

a. Oral or anterior
end. b. Posterior end.
c. Post-oral arms, d, e,
/, g. Spicular skeleton.
i. Intestine, m. Mouth.
o. Arms. oe. (Esopha-
gus, s. Stomach.

b. At the end of the next thirty-six hours, the larva
which is shown in ventral view in Fig. 63, and in side

112

HANDBOOK OF INVERTEBRATE ZOOLOGY.

view in Fig. 64, has undergone very considerable changes,
and is now sufficiently transparent to allow the internal
organs to be more minutely examined.

The ends of the ciliated ridge
have grown forward so as to form
a pair of ear-like processes (Figs.
63 and 64, c, c), the rudiments of
the pair of post-oral arms. The
' 0 cells of the ridge have become
thickened, columnar, and very dif-
ferent in appearance from the ordi-
nary ectoderm cells. They carry
long cilia, and are arranged in a
row which runs out to the tips of
the arms, and after bending around
them, turns towards the dorsal sur-
face, and bending forward, runs
along the free edge of the oral
lobe (a).

Great changes have also taken
place in the spicular skeleton,
which is now quite well developed.
The rods (d), which run into the
posterior lobe, and which we may

of call the lateral spicules, nearly
thesamela™ (Drawnfrom ^ other the median

nature by W. K. Brooks. )

line, and their free posterior ends

have enlarged into irregular, club-shaped masses. The
two branches which, at an earlier stage, ran towards the
middle of the ciliated ridge, have met and united so as to
form a solid bar (c), which may be called the ventral
transverse rod, and which crosses the ventral surface.
The branches which, at an earlier stage, ran towards the

FIG. 64.
FIG. 64. — Side

EMBRYOLOGY OF ECHINODERMS. 113

oral lobe, have lengthened so much that their tips (/"), are
visible in a ventral view. They are to become the spicules
of the pre-oral arms. The fourth branch (g), is now double,
and forms a fork, which runs nearly to the tip of each post-
oral arm.

The digestive tract is now quite complicated. The
mouth (m), which has been formed by the union of the
integument to the wall of the digestive tract, is situated
in the depression between the ciliated ridge and the oral
lobe (ct). It communicates through a short ossophagus (o e),
with the large, flask-shaped, thick- walled stomach (s).
The anus (o), is now very small, and it no longer opens
directly into the stomach, but is joined to it by a smaller
tube, the intestine (£), which is seen in a ventral view be-
tween the body wall and the stomach.

e. In from twenty-four to forty-eight hours more the
larva will be found to have changed greatly, and it is now
sufficiently transparent to allow the internal structure to
be studied more easily. It is shown in Fig. 66, as it ap-
pears in a side view while swimming, and in Fig. 65 it is
shown in a dorsal view. The specimen shown in this
figure was a little flattened by the pressure of the cover
jH'iss which was used to confine it.

The post-oral arms (c, c), have grown so much that they
now make about half the total length of the body, and
the two spicules (^), which form the skeleton, have united
to each other at intervals so as to form a ladder-like
structure, with two long sides, and a number of cross-
bars. The pigment spots are now very large and con-
spicuous, and there is a longitudinal row of them along
each arm.

The outer angles of the oral lobe (a), are fashioned into
a pair of ear-like processes (a1 a'), the rudiments of the

114

HANDBOOK OF LNVEKTEBKATE ZOOLOGY.

Fro. 65. D-

FIG. 65. — Dorsal view of a larva a little older, slightly flattened by
pressure. (Drawn from nature by W. K. Brooks. )

a. Anterior end. b. Posterior end. c, c. Post-oral arms, a' a'. Pre-
oral arms. d. Spicules of side of body. e. Ventral transverse spicule,
seen through body. /. Spicule of pre-oral arm. y. Spicule of post-oral
arm. i. Intestine, pushed to one side by pressure, k. Point where
lateral arm is to be developed. I. Rudiment of a dorsal transverse
spicule. m. Mouth, in, e. Mesoderm. ce. (Esophagus, p. Spicular
skeleton at posterior end of body. s. Stomach, w. Water tubes.

EMBRYOLOGY OF ECHINODERMS.

115

pre-oral arms, and the spicules which run into this lobe
bend forward at/", or run into
these arms to form their sup-
porting frame work.

At the point where the spic-
ule (/), bends forward, it gives
rise to a very small process (7),
which points towards the mid-
dle of the dorsal surface, and is
to become a transverse dorsal
bar. In a dorsal view at this
stage it is easy to see that the
ciliated ridge which fringes the
post-oral arms (c), bends back
towards the dorsal surface at
k, and runs forward along the
edge of the oral lobe («), and
pre-oral tentacles («' a'). It
therefore forms a closed circlet
around the mouth. The pos-
terior end (6), of the body is
now quite transparent, and the
ends of the two long, lateral
spicules (c?), have fused with
each other, thus forming a
large, irregular, perforated
mass (^>), which is covered
with small pigment spots.

The different regions of the

digestive tract are much more

FIG. 66.

FIG. 66. — Side view of a larva
sharply distinguished than they at the same stage, while swim-
were at earlier stages. The ™inf; <Dra™ from nature by

W. K. Brooks.)

mouth (m), is a large, circular Letters as in Fig. 65.

116 HANDBOOK OF INVERTEBRATE ZOOLOGY.

opening, fringed with cilia, and it has moved from its
primative position nearly to the anterior edge of the ven-
tral surface of the oral lobe. In a dorsal view it is visible
through the oral lobe.

The oesophagus (oe), is a long, thick-walled tube, lined
with cilia, and communicating, through a constricted open-
ing, with the large, globular, thick-walled stomach. The
intestine (£), is an elongated, thick-walled tube on the ven-
tral surface of the stomach, but the pressure to which the
specimen shown in Fig. 65 wras subjected has thrown it
onto one side. At this stage the mesoderm (we), may be
made out as a layer of irregular cells lining the body cav-
ity, and covering the digestive tract.

On each side of the oesophagus, near the point where it
joins the stomach, notice a pair of small, transparent
bodies, the water-tubes (w). It is extremely difficult to
follow the history of these important parts in Arbacia, but
much easier to trace them in the transparent larvte of
Strongylocentrotus, where they may be seen at a much
earlier stage.

d. A larva about twenty-four hours older is shown in
dorsal view in Fig. 67. The shape of the body is about
the same as in the preceding stage, but as Fig. 65 was
drawn from a compressed specimen, while Fig. 67 was
drawn from one which was swimming freely in the water,
the figures show considerable difference of outline.

At this stage, notice especially the increased length of
the pre-oral («', «'), and post-oral (c, c), arms ; the formation
of a little prominence (».), on each side in the angle between
these arms ; the increased length of the dorsal tran.-\ er>e
spicules (?), which were only small spines at the last stage ;
the division of the oesophagus into two chambers ; and the
lengthening of the water-tubes (w). At this stage, the

EMBRYOLOGY OF ECHINODEKMS.

117

FIG. 67.

FIG. 67. — Dorsal view of a slightly older larva. (Drawn from nature
by W. K. Brooks.)
a, a', b, c,f, I, m,p, s, audio. As in Fig. Go. 7;. Ku liment of lateral arm.

118 HANDBOOK OF IXVEKTEBRATE ZOOLOGY.

posterior end of that water-tube which is on the right side
in the figure may be seen to be united to the integument
of the dorsal surface of the body. Careful examination
will show that the body cavity is now filled Avith small,
transparent, branched connective tissue corpuscles, which
run across in all directions from the wall of the digestive

tr.'ict to the inner surface of the body wall.

e. At the end of the next forty-eight hours, the larva
which is shown in ventral view in Fig. 68, has changed

O •

its form, and the proportions of parts in several partic-
ulars, but the general structure is about the same.

The mouth (wi), is now situated on the middle of the an-
terior edge of the oral lobe («), instead of on its ventral
surface, and a ciliated ridge- , with a prominence (#"), at
each end, has been developed along its ventral edge.

The two pairs of pre-oral arms (a), and post-oral arms,
(c, c), are lengthened, and the tips of the latter pair are
almost covered with reddish-brown pigment spots. The
most marked change of form is due to the fact that the
lateral angles (w), between the two pairs of arms, have
travelled backwards nearly to the posterior end of the
body.

The rudimentary arm (n), in this angle is scarcely larger
than it was at the last stage, but the rudiments of a fourth
pair of arms, the dorsal, lateral arms (<?), have appeared
between the angles and the pre-oral arms («')•

Careful comparison of the larva; at this stage with the
figures of earlier stages will show great changes in the
form and position of the spicules. The mass (p), formed
by the fusion of the posterior ends of the lateral spicules (c?),
is undergoing resorbtion, and is now much smaller than it
has been. The bar (e), which during the early stages
ran across the ventral surface close to the edge of the cil-

EMBRYOLOGY OF ECHINODEKMS.

119

iated ridge, and which at the stage shown in Fig. 65, lies
at the point where the oesophagus joins the stomach, is

FIG. 68.

FIG. 68. — Ventral view of an older larva. (Drawn from nature by
W. K. Brooks.)

a, a', b, c, d, e, f, y, i, m, oe, p, and s. As in Fig. 65. a". Lip.
n. Point where ventral lateral arm is to be developed.

now pushed back so that it lies on the ventral surface of
the posterior half of the stomach.

120

HANDBOOK OF INVERTEBRATE ZOOLOGY.

It will be remembered that this bar was formed by the
union of two processes which met and united in the me-
dian line. At this stage they separated again at this
point on the slightest pressure, and a specimen may occa-
sionally be found with quite a wide gap on the middle
line.

~ c.

FIG. 69.

FIG. 69. — Ventral view of an older larva.
W. K. Brooks.)

Letters as in Fig. 68.

(Drawn from nature by

/. In from twenty-four to thirty-six hours more, the
halves of the bar (Fig. 67, e), are widely separated, and
are partially resorbed, and the posterior ends of the spio

EMBRYOLOGY OF ECHINODEEMS. 121

ules (d) are also separated from each other, and nearly
resorbed. The pre-oral and post-oral arms are somewhat
longer than before, and more pigmented. The process (n)
of Fig. 68, in the lateral angle of the ciliated ridge, is
now a short, club-shaped arm (Fig. 69, n), thickly covered
with small pigment spots, and containing a small, needle-

FIG. 70.

FIG. 70. — Dorsal view of an older larva. (Drawn from nature by
W. K. Brooks. )

t. Spicule of dorsal lateral arms. Other letters as in Fig. (39.

like spicule. The process (q) is a little longer than before,
but it is not yet a distinct arm, although traces of a small,

122 HANDBOOK OF INVERTEBRATE ZOOLOGY.

ladder-like spicule may be detected in it by careful exam-
ination. The intestine is very much smaller than it was
at the preceding stage, and it now joins the anterior edge,
instead of the ventral surface of the globular stomach.

g. The larva forty-eight hours older is shown in dorsal
view in Fig. 70. The arms (n) have lengthened slightly,
and their spicules (>•) have formed a bridge across the dor-
sal surface of the body, close to the posterior end. The
posterior ends of the spicules (d) have almost disappeared.
The arms (q) have lengthened, and an elongated, ladder-like
spicule has appeared in each of them. The lateral angle
between the pre-oral and post-oral arms, now occupied
by the arm (n) is almost at the posterior end of the body.
This change of position is due in part to the excessive
growth of the organs anterior to the dotted line (a;) in
part to the absorption of organs posterior to this line, and
in part to the movement of the angle (?i) of Figs. 67 and
68 towards the posterior end.

Notice that a new spicule (u*) makes its appearance on
the middle line of the dorsal surface over the oesophagus
at about this stage.

b. The fully developed pliiteus.

This is shown in dorsal view in Fig. 71, and in ventral
view in Fig. 72. In Fig. 73, the spicular skeleton is
shown in its natural position, but without the soft parts.

Notice that the dorsal and ventral lateral arms (71 and
72, q and n) are now fully developed, and are supported
by long spicules (r and t). The spicules (r) of the ventral,
lateral arms are simple, and their inner ends meet on the
median line to form a transverse bar (?•) which carries at
each end, where it joins the brachial portion, a short
spine (w>) , which runs forwards and outwards.

The spicules (t) of the dorsal, lateral arms are ladder-

EMBRYOLOGY OF ECHINODERMS.

123

like ; and long, perforated spines (x) run from their prox-
imal ends inwards and forwards over the dorsal surface
of the stomach. A similar process (e) is sent inwards and
forwards over the ventral surface of the stomach from the

FIG. 71. — Dorsal view of the fully developed pluteus of Arhacia
punctulata. (Drawn from nature by Mr. B. P. Colton.)
For explanation see Fig. 73.

124

HANDBOOK OF INVEIITEBKATE ZOOLOGY.

spicule (d) of the post-oral arm (c). The spicules (f) of the
pre-oral arms (af) are now very long, and they reach nearly
to the posterior end of the body.

A great fold or lip (Fig. 72, o I), now runs downwards
from the anterior end of the body towards the ventral

FIG. 72.

FIG. 72. — Ventral view of the fully developed pluteus of Arbacia.
(Drawn from nature by Mr. H. Ganuan.)
For explanation see Fig. ":).

EMBRYOLOGY OF ECHINODEIiMS.

125

FIG. 73.

FIG. 73. — Ventral view of the spicular skeleton of the fully developed
pluteus of Arbacia punctulata. (Drawn from nature by Mr. H. Garman. )

Letters of reference for Figs. 71, 1'2, and 73.

a Anterior end of body. "'. Pre-oral arms, a", a"' Secondary oral
anus, a b. Amhulacral feet of young sea-urchin, b. Posterior end of
body. c. Post-oral arms. d. Lateral spicules of body. e. Transverse
ventral spicules. /. Spicules of pre-oral arms. g. Spicules of post-oral
arms. i. Stomach. //*. Mouth, n. Ventral lateral anns. o. Anus.
o I. Oral lobe. q. Dorsal lateral arms. ?•. Spicules of ventral lateral
arms. s. Stomach. t. Spicules of dorsal lateral arms. u. Median
dorsal spicule. v. Posterior transverse bar. w. Spine from spicule r.
.c. Spine from spicule t.

126 HANDBOOK OF INVERTEBRATE ZOOLOGY.

surface, and hangs over the mouth. The anterior edge
of this lip is prolonged into two pairs of secondary oral
arms (a" and «'"), those nearest the middle line being
much the smallest.

The median dorsal spicule (M) which appeared at the
last stage, has now lengthened, to form a large £7, which
lies on the dorsal surface, and sends a branch into each of
the outer secondary oral lobes.

On the ventral surface of the body (Fig. 72), the ciliated
ridge has grown backwards on each side, between the
post-oral lobe and the bases of the post-oral arms, to
form a pair of ear-like processes (auf), which are fringed
with cilia.

On the dorsal surface (Fig. 71) a similar pair of ear-
like processes (an} have been formed by the development
and folding of two lines of ciliated cells, one on each
side of, and parallel to the middle line of the body.

At this stage, the stomach is slightly pushed to one
side by the development of five hollow tubes (Figs. 71
and 72, a b), on one side of it. These are the first five
tubular ambulacra of the young sea-urchin, and they are
on the right side of the stomach in a dorsal, on the left in
a ventral view.

In the star-fish larva, where their origin can be more
satisfactorily studied, it will be seen that they are devel-
oped from the left water-tube, and not from the actual
walls of the stomach.

i. The development of the young sea-urchin.

As the development of the young echinoderm within
the larva can be studied to more -advantage in the star-fish
than in the sea-urchin, its formation will be more fully
described under that heading, but the following points
should be noticed in the pluteus of Arbacia.

EMBRYOLOGY OF ECHINODEKMS.

127

FIG. 74.

FIG. 74. — Pluteus, with young sea-urchin, seen from the ventral sur-
face. (Drawn from nature by Mr. H. Garman.)

a. Anterior end of body. a'. Pre-oral arms, a'', a'". Secondary oral
arms. a b. Ambulacral feet of sea-urchin. a u. Ventral auricular
process. 6. Posterior end of body. c. Post-oral aims, c, e, b. Ab-oral
surface of sea-urchin, n. Ventral lateral arms, o I. Oral lobe. q. Dorsal
lateral arms. s. Stomach.

128 HANDBOOK OF INVERTEBRATE ZOOLOGY.

The larva soon becomes asymmetrical, as shown in
ventral view in Fig. 74, and the pre-oral arms («') begin
to disappear, while the dorsal, lateral arms (q) become
longer than any of the others.

A large circular opening makes its appearance on the
right side of the body (ventral view), between the bases
of the post-oral arm (c) and the dorsal, lateral arm (q) and
through this opening the ambulacra] feet (a b) of the sea-
urchin may now be protruded. They are five in number,
one for each ray of the sea-urchin, and around them there
is a circle of fifteen flattened, perforated plates, the first
set of spines of the young sea-urchin.

The stomach (s) is now pushed over on to the left side
of the body, and a granular belt (ech) with pigment
spots, around its right side, indicates the position of the
developing body-wall of the ab-oral surface of the sea-
urchin. The pluteus now becomes still more distorted, and
in about twenty-four hours it assumes the form shown in
Fig. 75, which is a dorsal view. The mouth and pre-
oral arms (a', a") of the pluteus are pushed to the left,
and the growing sea-urchin now fills nearly the whole
body. The two ventral, lateral arms (n, n) are nearly
parallel to each other, and the post-oral arms (c) and dor-
sal, lateral arms (q) are thrown back towards the posterior
end of the body. The five ambulacral feet are now pro-
truded from the surface of the body, and a disc of small,
calcareous plates appears in the sucker with which each
of them ends. Between their bases are the fifteen spines,
(s), arranged in five sets, of three each.

For some time the larva is able to bend back the arms
as shown in the figure, and, protruding its feet, to crawl
as an echinoderm ; or, pulling back the feet, and pushing
the arms into their original position, to swim as a pluteus.

EMBRYOLOGY OF ECHINODERMS.

129

The mouth of the echinoderm is now formed as a new
opening, which penetrates to the stomach of the pluteus
from the right side of the body, in the centre of the circle
of ambulacral feet.

FIG. 75.

FIG. 75. — The same, a little older, from the dorsal surface,
from nature by Mr. B. P. Colton. )
Letters as in Fig. 74.

(Drawn

The sea-urchin grows and protrudes more and more
from the opening, and the arms of the pluteus are finally
bent upwards so as to project from the ab-oral surface of
the body, as shown in Fig. 76. The integument of the
larva still covers the sea-urchin as a delicate, transparent,
outer skin, and the oral lobe can still be recognized for a
short time. The manner in which the arms finally disap-
pear is somewhat peculiar. The wall of the arm flows,
like a retracted pseudopodium, down onto the surface of
the body, leaving the bare spicule projecting from the
ab-oral surface. The spicules soon drop off, the dentary
apparatus is developed, and the young sea-urchin assumes
the form shown, from the oral side, in Fig. 77.

130 HANDBOOK OF INVERTEBRATE ZOOLOGY.

VI. The swimming larva of the starfish.

The larvae of starfish, which are known as Bipinnaria and
Brachiolaria, are constructed on essentially the same plan
as the pluteus of the sea-urchin, although there are great

FIG. 76.

FIG. 76. — The sea-urchin, with the arms of the pluteus disappearing.
(Drawn from nature by Mr. B. P. Colton. )

differences in details of structure. They may usually be
obtained at the surface of the ocean in early summer with

EMBRYOLOGY OF ECHENODERMS.

131

the tow-net or dip-net, and since their greater size renders
them much more fit than the pluteus for studying the
mode in which the young echinoderm is formed inside the
larva, the student should if possible rear some of them in
small aquaria, and study the development of the young
starfish. The full-grown larva is about one-twelfth of an

FIG. 77.

FIG. 77. Oral surface of the young sea-urchin,
by Mr. H. Garman. )

(Drawn from nature

inch long, transparent, and of the shape shown in Fig.
78. This figure shows the bipinnarian larva of a southern
starfish, but the brachiolaria of our common species is
almost exactly like it, and the student should have no
difficulty in recognizing it when captured.

132

HANDBOOK OF INVERTEBRATE ZOOLOGY.

a. The structure of the larva.

At first sight there seems to be little likeness between
the starfish larva (Figs. 78 and 79), and the pluteus of
a sea-urchin, but more careful examination shows that

FIG. 78.

FIG. 78. — Bipinnarian larva of starfish, as seen in ventral view.
{Drawn from nature by E. B. Wilson. )

a. Anterior end. a'. Pre-oral arras, b. Posterior end. 1. Pre-oral
ciliated ridge. 2. Post-oral ciliated ridge. 3. Anterior median ventral
lobe. 4- Anterior median dorsal lobe. c. Post-oral arms. i. Intestine.
m. Mouth, n. Lateral arm. o. Anus. oe. (Esophagus, q, q.' Dorsal
lateral arms. s. Stomach, ww'. Water tubes, am. Flattened poste-
rior end of left water tube.

EMBRYOLOGY OF ECHINODERMS.

133

they are much alike. The mouth of the pluteus is at the
anterior end of the body, while the anterior end of the
body of the starfish larva is elongated into a long lobe
(Fig. 78, a), and the mouth (m) is about midway between

FIG 79.

PIG. 79. — Dorsal view of the same larva. (Drawn from nature by
E. B. Wilson.)

Letters as in Fig. 78.

the anterior end (a), and the posterior (b) on the ventral
surface. It lies, as it does in the sea-urchin pluteus, in a
furrow, with a ciliated ridge (1) in front of it, and an-
other (2) between it and the anus (o). The long O3sopha-

134 HANDBOOK OF INVERTEBRATE ZOOLOGY.

gus (oe), the globular stomach (*), and the ventral intes-
tine (i), are very similar to those of the pluteus.

The ciliated ridges (1 and 2) before and behind the
mouth, are prolonged into a number of paired lateral
arms, but these are shorter and more numerous than those
of the pluteus, and they have no supporting skeleton.

In the pluteus the ciliated ridge which passes in front
of the mouth, fringes the pre-oral arms, and then, run-
ning back onto the lateral arms, fringes the post-oral arms,
and then passes across the ventral surface behind the
mouth, so that its course forms a single closed circlet.

In the bipinnaria the pre-oral ciliated ridge (7), after
fringing the pre-oral arms (a'), runs forward on each side
to form a lobe (Fig. 78, 3) on the ventral surface of the
large oral lobe (a). It thus forms a small closed circlet on
the ventral surface in front of the mouth, and encloses a
surface which is entirely ventral, and which is known as
the pre-oral plastron.

The ciliated ridge (J?), which passes between the mouth
and the anus, becomes bent into a pair of arms (c), which
ans\ver to the post-oral arms of the pluteus. It then runs
backwards on each side to form a pair of lateral arms (n),
and then runs forward along the edges of the dorsal sur-
face (Fig. 79), folding out to form two pairs of lateral
dorsal arms (q and q'}. The two sides finally meet at the
tip of the dorsal surface of the anterior lobe (a), where
they form an unpaired lobe (Fig. 79, 4}. This circlet
surrounds an area partly ventral and partly dorsal, and
known as the anal plastron. There are thus two closed
circlets of cilia in the starfish larva, instead of one as in
the sea-urchin, and one of these is in front of the mouth
and on the ventral surface, while the other runs between
the mouth and the anus, and fringes the dorsal surface.

EMBRYOLOGY OF ECHINODERMS. 135

The larva shown in the figures is known as a Bipinnaria.
A Brachiolaria is a larva of the same type, but with a
system of fleshy, unciliated arms, known as brachiolar
arms, at the anterior end of the body, between the loops
3 and 4.

b. The water-system of echinoderm larvae.

Before the mouth (Fig. 62, m) joins the stomach (o),
two little pouches, the water-tubes, or peritonseal vesicles,
are constricted off from the stomach, at the point where
the oesophagus is to unite with it. After the ossophagus
joins the stomach one of these lies on each side of it as in
Fig. 65, w). They then lengthen as shown in Fig. 67, w,
and the tip of the one which is on the left in a ventral
view unites to the integument of the dorsal surface of the
body, and forms an external opening there.

The two water-tubes now lengthen, as shown at w w' in
Figs. 78 and 79, and run backwards onto the sides of the
stomach, where they form a pair of flattened pouches.
They also run forward, and bending towards each other
in front of the mouth, unite to form a single large pouch
(Figs. 78 and 79, ww').

c. The formation of the echinoderm in the body of the
larva.

The flattened portion of that water-tube which lies on
the left of the stomach (Fig. 78, am), now becomes
folded out to form five lobes (Fig. 80, am) ; Fig. 81,
am1, am1, am3, am4, am5), which are to become the
water-tubes of the five rays of the starfish. These five
lobes are arranged in a rosette, with the one which is to
belong to the anterior ray of the starfish (am3) pointing
towards the posterior end, and those which are to belong
to the two rays of the bivium (am1, am6), slightly sepa-
rated from each other.

136

HANDBOOK OF INVERTEBRATE ZOOLOGY.

FIG. 80.

FIG. 80. — Ventral view of an older larva. (Drawn from nature by
E. B. Wilson. )

am. Ambulacral area of developing starfish, ab. Ab-oral area of
developing starfish, ab1, ab6. Its free ends.

Other letters as hi Fig. 78.

EMBRYOLOGY OF ECHINODERMS.

137

On the outer surface of the corresponding portion of
the opposite, or right water-tube, and therefore on the
opposite side of the stomach, calcareous spicules make
their appearance, and build up a spiral band (ab), which

FIG. 81.

FIG. 81. — Side view of the same larva. (Drawn from nature by E. B.
Wilson.)

am1, am2, am8, am*, am5. The five water tubes of starfish.
Other letters as in Fig. 80.

138

HANDBOOK OF INVERTEBRATE ZOOLOGY.

is to form the integument of the upper surface of the body
of the starfish. The extremities of this band (abl and
a&5, Fig. 80) are widely separated, and it is divided into
five lobes, corresponding to the five rays, each lobe being
again divided into four smaller lobes.

The upper and lower surfaces of the future echinoderm
are thus seen to be on the right and left sides respectively
of the stomach of the larva. They include between them
part of the right water-tube, which i.s to become the body

FIG. 82.

FIG. 82. — Ab-oral surface of very young starfish. (Drawn from na-
ture by E. B. Wilson. )

cavity of the starfish ; part of the stomach, which is to
become the digestive tract of the starfish ; and part of the
left water-tube, which is to become the water-system.

d. The young starfish.

These portions grow and fold towards each other ; a new
mouth is formed in the centre of the rosette on the left

EMBRYOLOGY OF ECHINODERMS.

139

side of the larva ; the body of the larva is absorbed or cast
oft', and the young starfish escapes, in the form shown
from above in Fig. 82. In this figure 1 is the anterior
ray, and 4 and 5 the two rays which were at the ends
of the spiral band in the larva. The calcareous skeleton
develops rapidly, and the sucking feet grow out from the
water-tubes, as shown from below in Fig. 83. Notice that

FIG. 83.

FIG. 83. — Oral surface of the same starfish, a few days older. (Drawn
from nature by E. B. Wilson.)

the radiating water-tubes are, at this stage, internal, and
covered by the skeleton, as in the adult sea-urchin, and
that there are no ambulacra! furrows.

140 HANDBOOK OF INVERTEBRATE ZOOLOGY.

XV.— THE GENERAL ANATOMY OF THE EARTH-

WORM.

(Lumbricus.)

I. EXTERNAL FORM.

The external characteristics may be studied in an alco-
holic specimen, or one which has recently been killed with
ether. If alcoholic specimens are used, they should be
placed in water for a few hours. The various reproduc-
tive apertures are much more conspicuous in some speci-
mens than in others, according to the sexual condition of
the animal, and if there is difficulty in finding them in one
specimen, another may be tried. Their positions vary
somewhat, according to the species, and the numbers
given here apply to L. terrestris, but any other species
will answer for examination.

In the examination of the external form, notice :

1. The long, cylindrical body, divided by contrictions
into rings, or segments, of which there may be as many as
three hundred and fifty.

2. The anterior end, or that at which the segments are
largest.

3. The brownish-red, slightly iridescent, dorsal surface.

4. In the median dorsal line, the bright-red, dorsal
bloodvessel may be seen through the integument, and in
a small, transparent, living animal, irregular pulsations of
this vessel can be detected.

5. The ventral surface is of a much lighter color, and
more iridescent than the dorsal.

6. At a point about one-third the length of the body
from the anterior end, notice a thick, glandular white ring
or saddle, the girdle, or clitellus, which is formed by the

ANATOMY OF THE EARTHWORM. 141

thickening of the dorsal and lateral portions of about
seven segments from the twenty-ninth backwards. The
ventral portions of these segments are much less special-
ized than the upper portions.

7. The delicate, chitinous, transparent cuticle which
loosely invests the external surface of the animal, and
which may be slipped off from a specimen which has lain
for a few hours in water.

8. The locomotor spines, or setae. In the earthworm,
these are so small that a lens is needed to detect them,
but if a worm be pulled backward gently between the
fingers, the resistance offered by the setae can be felt.
They are arranged in four longitudinal double rows, two
rows on each side, along the ventral surfaces of all the
segments except the first, second, third, fourth, and last.

The outer pair are on the line where the dark-colored
dorsal region shades off into the lighter-colored ventral,
and the inner pair are a little nearer the ventral median
line.

9. The mouth is at the anterior end ot the body, and
leads into a large, eversible, buccal pouch. If a living
earthworm be held gently between the fingers, near the
anterior end of the body, the animal can be made to evert
this pouch.

10. The anus, a small aperture at the posterior end of
the last segment.

11. The segments and apertures of the body.

a. The first segment is not a complete ring, and forms
a proboscis, or upper lip.

b. The remaining segments are complete rings, and are
alike as far as the ninth.

c. The ventral portions of the ninth, tenth, and eleventh
segments are thickened so as to form white glandular

142 HANDBOOK OF INVERTEBRATE ZOOLOGY.

prominences, which arc used as organs of adhesion during
the act of copulation. The two pairs of inner setae of
each of these segments are situated near the outer ends of
these prominences, and are larger than those of the adja-
cent segments.

d. On the sides of the body, in a line with the outer
setae, and between the ninth and tenth, and tenth and
eleventh segments, are the external apertures of the four
seminal receptacles.

e. On the fourteenth segment, just exterior to the setae
of the inner row, are the openings of the oviducts. These
are very small, but, in a large specimen, they may be seen
with a lens after the cuticle has been removed.

f. On the fifteenth segment, just outside the inner
setae, are two somewhat prominent papillae, each of which
has a slit-like aperture, the orifice of the vas deferens, or
male reproductive aperture.

g. Segments twenty-nine to thirty-six have already
been noticed as the girdle. Posterior to the thirty-sixth,
the segments suddenly decrease in width, and are then
repeated, with little modification, to the posterior end.

h. On the median dorsal line there is a row of pores,
one on the anterior margin of each segment, by which the
body-cavity opens externally.

II. GENERAL ANATOMY.

A large specimen should be selected for dissection, and
killed by placing it for a few minutes in a bottle or tum-
bler with a few drops of ether. With a sharp knife or a
pair of fine-pointed scissors make an incision along the
median dorsal line, and pin out the integument of the
anterior third of the body, under water.

1. The perivisceral fluid.

The body cavity will be found to contain, especially in

ANATOMY OF THE EARTHWORM. 143

the posterior segments, a milky fluid, the perivisceral
fluid. Place a drop of the fluid on a glass slide,
gently cover it, and examine it under a microscope.
It consists of a coagulable, albuminous plasma, which
contains great numbers of transparent, granular, amoeboid
corpuscles. In addition to these normal constituents, it
usually contains foreign bodies, such as Gregarinee, para-
sitic Infusoria, and Xematoid worms, broken setae, etc.

2. The muscular dissepiments, or diaphragms, which
extend inwards from the integument to the wall of the
digestive tract, and imperfectly separate the body cavities
of adjacent segments.

3. The digestive tract, a nearly straight tube, without
convolutions, extending along the median line of the body
from the anterior to the posterior end.

4. Upon its dorsal surface, and closely united to its
wall, observe the red dorsal or supra-intestinal blood-
vessel.

5. The digestive tract is divided into several well-
marked regions : —

a. The pharynx, a large, broad, muscular organ (Fig.
84, ?i), extending from the second to the seventh seg-
ment, and similar, in shape and connections, to the suck-
ing chamber of the leech.

(i.) The radiating muscular fibres which bind it to the
integument.

(ii.) The cephalic or supra-cesophageal ganglia; two
pear-shaped bodies (Fig. 84, a), upon the dorsal surface
of the pharynx, in the third segment of the body, and
united to each other by their broad ends upon the dorsal
median line.

From their smaller outer ends arise two fibres, which
pass down around the pharynx to unite with the ventral
nerve chain.

144

HANDBOOK OF INVERTEBRATE ZOOLOGY.

b. The oesophagus; a long, nearly straight, thin-walled,
elastic tube, much smaller than the pharynx, and extend-
ing from the eighth to the sixteenth segment (Fig. 84, c, d).
It is slightly constricted at the points where it passes
through the partitions between the segments, and its mus-
cular fibres are continuous with those of the partitions.

(i.) In the tenth, eleventh,
and twelfth rings, the white
testes (Fig. 84, k), surmount
and overlap the oesophagus.

(ii.) If these are carefully
displaced, three pairs of
high ly vascular pouches
(Fig. 84, e), the cesophayeal
glands, will be seen between
them, projecting from the
sides of the oesophagus.

FIG. 84. — The anterior end of the
earthworm, opened along the dorsal
surface, to show the digestive organs.
(From Lankester, Anatomy of the
Earthworm. Quar. Jour. Mic. Sc.,
1864, P. VII., Fig. 5.)

1, 2-19. The nineteen anterior
segments. a. Cerebral ganglia.
6. Pharynx, c. (Esophagus, d. Pos-
terior portion- of it. e. (Esophageal
glands. /. Crop. </. Gizzard.
h. Dorsal blood-vessel. L Aortic
FIG. «. arches, k. Testes. I. Intestine.

The first pair are a little larger than the others, and if
they are removed from the oesophagus, and opened upon
a slide, and examined with a microscope, they will be
found to contain solid crystalline bodies, which dissolve,
with active effervescence, when treated with acid.

ANATOMY OF THE EARTHWORM. 145

c. At about the sixteenth segment, the digestive tract
suddenly dilates, and forms a large, muscular, highly
vascular, heart-shaped crop (Fig. 84, y), which, in the
living animal, usually exhibits muscular contractions, even
when the animal has been opened.

d. Immediately succeeding the crop is the "gizzard"
(Fig. 84, g), a firm-walled, cylindrical, highly vascular
chamber.

e. This is followed by the intestine (Fig. 84, /), which
passes to the posterior end of the body with very little
modification. Its walls are greatly folded and sacculated,
especially in the anterior portion.

/. A layer of brownish-green, delicate, easily-ruptured
glands, the hepatic glands, which cover the dorsal surface
of the intestine, and surrounding the dorsal blood-vessel,
extend as far forward as the oesophagus.

6. The dorsal blood-vessel. This extends along the
dorsal surface of the digestive tract, in contact with its
walls, as a distinct vessel (Fig. 84, h], from the poste-
rior end of the body to the anterior end of the oesopha-
gus, where it breaks up into a number of smaller vessels,
which ramify upon the pharynx and oesophagus.

In the living animal, the mam trunk may be seen to
dilate and contract at intervals, but no part of it is modi-
fied to form a special pulsating organ. It gives rise, at
intervals, to large lateral trunks, which pass outward and
downward around the digestive tract to join the infra-
intestinal vessel. These arches are very large and promi-
nent in the eighth to the thirteenth segments, and are here
furnished with small, saccular, pulsatile dilations.

The dorsal vessel also gives rise to smaller lateral ves-
sels, which pass to the muscular partitions, and to the
integument and digestive organs.

146 HANDBOOK OF INVERTEBRATE ZOOLOGY.

a. Cut the dorsal vessel, and place a drop of the red
fluid on a slide ; note that it coagulates quickly. Cover
another drop, and examine with a microscope. It is a
clear, red fluid, which contains small, flattened, oval or
fusiform colorless corpuscles, much smaller, and with
sharper, more regular outlines than those from the body
cavity.

The digestive tract may now be cut off posterior to the
pharynx, and removed from the body, in order to expose
the organs which lie below. Great care is necessary to
avoid injuring the testes while removing that part of the
oesophagus which lies between them.

If a fresh specimen has been used, it should now
be. covered with strong alcohol, in order to coagulate
and harden the delicate transparent portions of the
body.

7. The nervous system. This is made up of: —

a. The cerebral ganglia, which, as has been pointed
out, are situated upon the dorsal surface of the pharynx
in the third segment (Fig. 84, a; Fig. 84, h).

(i.) A large nerve may be traced forward from each
half of the cerebrum (Fig. 87, i). These nerves soon
divide into smaller branches, which pass to the anterior
segments, especially the first.

(ii.) From the outer ends of the cerebrum two com-
missures (Fig. 87, d,) pass outward and downward around
the oesophagus to unite with the ventral chain.

(iii.) Four or five nerves may be seen to run backward
from the upper portion of each half of this collar (Fig.
87, g). They soon penetrate the muscular walls of the
pharynx, and their terminations cannot be made out with-
out further dissection.

ANATOMY OF THE EARTHWORM.

147

c 'a c

Fio. 85.

FIG. 85. — Diagram of the ventral surface of the body cavity of the
eighth to twentieth segments of the earthworm. (Drawn by W. K.
Brooks. )

8, 9, 10-26. Body cavities of the segments. a. Nervous system.
b. Nerves from ganglia, c. Nerves from commissures, d. Diaphragms
between the segments, e. Receptacula seminis. /. Testes. fir. Vesicula
seminis. h. The opening of the vasa defercntia, represented as seen

148 HANDBOOK OF INVERTEBRATE ZOOLOGY.

through the vesicula seininis. i. Convoluted portion of vas deferens.
k. Vas deferens. k'. Its external opening in the fifteenth segment.
I. Ovaries in the thirteenth segment, m. Oviducts in "the fourteenth
segment, n. Enlarged setigerous glands in the eighth to thirteenth seg-
ments, o. Ordinary external setigerous gland, o'. Ordinary internal
setigerous gland, p. Fibre connecting o and o'. q. Segmental organ.
r. Its internal orifice, s. Its external orifice, shown in the thirteenth,
fourteenth and fifteenth segments, from which the other parts of the
glands have been removed.

b. The ventral nerve chain. This is made up of : —

(i.) Two commissural cords, which run side by side,
and in contact, from the fourth to the last segment (Fig.
85, a; Fig. 87, a).

(ii.) A double or bilateral ganglionic enlargement
(Fig. 87 ; 5, 6, 7), in each segment posterior to the third.

(iii.) Two pairs of nerves (Figs. 85 and 87, 6), originate
in each ganglion, and pass to the muscles and viscera of
each segment.

(iv.) A pair of nerves originate in the commissure an-
terior to the ganglion in each segment, and supply the
posterior face of the muscular partition (Figs. 85, 87, i).

8. The segmental organs.

In each segment except the first, second, and third,
there is a pair of segmented organs (Fig. 85, #), each of
which consists of %\o

a. A ciliated funnel (Figs. 85, r, and 87), which is
attached to the anterior face of each dissepiment near the
median line. It is a small, funnel-shaped pouch, with a
wide, ciliated opening, which communicates with the body
cavity. A much smaller tubular neck passes through the
partition, and thus connects the funnel with

b. The glandular portion of the organ ; a long, greatly-
convoluted, delicate- walled tube (Fig. 86, «, b, c, d), lined
with cilia, and richly supplied with blood-vessels, and

ANATOMY OF THE EARTHWORM.

149

connected by a mesenteric membrane with the posterior
face of the partition.

c. The external opening (Figs. 85, s, and 87), on the
ventral surface of the segment which contains the glandu-
lar portion of the organ. It is a very small aperture just
outside the inner bunch of setae.

9. The reproductive organs.

These, in their order of succession, are —

1. The seminal receptacles ; 2. The
testes; 3. The seminal vesicle; 4. The
vasa deferentia ; 5. The ovaries ;
6. The oviducts.

a. The testes. Three pairs of large,
white, slightly vascular glands (Fig.
85, f), which project above and over-
lap the oesophagus in the ninth, tenth,
and eleventh segments. The two an-

- ^ ^ M

terior pouches unite with each other,
while the third is undivided.

F:o. 86. — Segmented organ of earthworm,
magnified twenty-five diameters, and freed from
the surrounding tissues.

1. Central end. 2. Anterior margin. 3. Peri-
pheral end. 4- Posterior margin, r. Opening
into body cavity — "ciliated funnel." s. Exter-
nal opening, a. Convoluted portion, b. Outer
fold. c. Inner fold. d. Muscular sac.

(i.) Cut off a piece from one of the testes, and place a
drop of the white fluid which it contains under the micro-
scope. In it will be found mother cells and spermatic
filaments in all stages of development.

b. The lower end of each testis is sharply constricted,
and united by a short neck to the seminal vesicle, a large,

150

HANDBOOK OF INVERTEBRATE ZOOLOGY.

white, membraneous pouch (Fig. 85, <?), which extends
across the median ventral floor of the tenth and eleventh
segments, and receives the testes of both sides of the
body.

c. On the lower surface of this organ, near the median
line, are the four ciliated, funnel-shaped openings of the
vasa deferentia (Fig. 85, /*), one on each side in the tenth,
and one on each side in the eleventh segment. They are
bound by connective tissue to the lower surface of the
seminal vesicle, but have no communication
with its cavity. The male fluid escapes
from the receptacle by the rupture of its
walls, and is then drawn by the cilia into
these funnels.

FIG. 87. — Anterior portion of nervous system of
earthworm. (From Lankester, Anatomy of the Enrlli-
worm, Quar. Jour. Mic. Sc., N. S., vol. V. P. vi.,
Fig. 6. ) Magnified about five diameters.

a. Commissural fibres, b, b, b, b. The two pairs of
nerves which arise from each ganglion, c, c. The nerves
which pass from the commissure to the diaphragm.
S, 6, 7, 8. The ganglia of the fifth, sixth, seventh, and
eighth segments, respectively, d. CEsopliageal collar.
e. Nerves from collar to the muscles of fourth segment.
/. Space occupied by pharynx, g. Nerves to pharynx.
h. Cerebral ganglia, i. Nerves to first segment.

FIG. 87.

d. The vasa deferentia may be traced as delicate, white
tubes running backward from the funnels (Fig. 85, k).
The four tubes are at first separate, but in the thirteenth
segment the pair on each side unite, and thus form two
ducts, which run backward between the inner ends of the
two rows of setae of each side, and open externally in
the fifteenth segment.

e. The seminal receptacles; four nearly spherical, va>-

ANATOMY OF THE EARTHWORM. 151

cular, white sacs, situated just outside the testcs, between
the ninth and tenth and the tenth and eleventh segments
(Fig. 85, e).

(i.) Remove one of them, and examine its contents
with the microscope. It will be found to be filled with a
compact mass of fully-developed spermatic filaments.

g. The detection of the ovaries and oviducts is a matter
of some difficulty. In a large specimen, which has been
pinned out under alcohol, on the ventral surface of the
thirteenth segment, close to the nerve cord, are a pair of
small, white, pear-shaped organs, about one-sixteenth of
an inch long, the ovaries (Fig. 85, ?).

They are attached by their stalks to the ventral body
wall, and a microscopic examination shows that they are
membraneous sacs, without ducts, and filled with ova, in
all stages of development. The ripe ova escape, by the
rupture of the walls, into the body cavity, and are then
taken up by the mouths of the oviducts.

h. The oviducts are a pair of small, trumpet-shaped,
ciliated tubes, which open externally by their small ends,
near the inner setae of the fourteenth segment (Fig. 85, m).
The inner, enlarged end of each oviduct bends forward,
passes through the partition between the thirteenth and
fourteenth segments, and opens in the cavity of the thir-
teenth segment by a large, funnel-shaped, ciliated mouth,
which is close to the ovary of the same side.

10. The integument. After the viscera have been re-
moved, the longitudinal muscles of the body wall may be
examined.

They consist of —

a. A large ventral band.

b. Two lateral bands.

c. A dorsal band.

152 HANDBOOK OF INVERTEBRATE ZOOLOGY.

11. The seligerous glands. Four of these may he seen
in each segment, projecting into the body cavity, between
the ventral and lateral, and lateral and dorsal muscular
bands (Fig. 85, o, o'). In the ninth, tenth, eleventh, and
sometimes in the eighth, twelfth, and thirteenth segments,
the glands of the inner setae are much enlarged, and form
conspicuous white pouches (Fig. 85, ri).

In the segments posterior to the thirteenth, a muscular
band, (p), will be seen running from the gland of the outer
to that of the inner setae.

XVI. — THE MICROSCOPIC STRUCTURE OF THE
EARTHWORM.

SPECIMENS for microscopic work should be hardened in
alcohol, by placing them in eighty per cent alcohol for
about twelve hours, and then transferring them to strong
or absolute alcohol.

Cut one of the specimens into sections about half an inch
long ; stain them in a very dilute solution of picro-carmine
for two or three hours, and then return them to the strong
alcohol to extract the water. Mount them in paraffine,
and cut a number of thin sections from each, as described
in Section V. Examining the sections with a power of
one hundred to two hundred diameters, notice : —

I. The body wall; which is made up of five concentric
layers.

a. The cuticle, or outer layer, is a delicate, transparent,
structureless layer (Figs. 88, a, and 89), which is perfor-
ated by fine canals or pores perpendicular to the surface.
It is loosely attached to the surface of the body, and is
very easily detached from a fresh specimen.

STRUCTURE OF THE EARTHWORM.

153

b. Examine the outer surface of a piece of cuticle which
has been stripped off from the body of a fresh specimen,
and notice the fine parallel lines which cause the iri-

FIG. 88.

FIG. 88. — Transverse section through the cesophageal region of the
body of Lumbricus terrestris, in the plane of a dissepiment. (Copied
with slight changes from Claparede. Histolof/ische Untersuchungen uber
den Rec/enwurm. Zeit. f. Wiss. Zool., xix. Taf. xliv. Fig. 1.)

a. Cuticle, b. Hypodermis. c. Circular layer of muscles, d. Layer
of longitudinal muscles, e. Dorsal band. /. Ventral band. g. Lateral
bands, h. Bands between setae, j. Circular muscular fibres around
oesophagus, k. Circular muscular fibres around nervous system. I. Cavity
of ossophagus. m. Cuticle of oesophagus, n. Epithelial layer of oeso-
phagus, o. Layer of circular muscles around oesophagus, p. Layer of
longitudinal muscles, q. Dorsal vessel, r. Ventral nerve cord.

154 HANDBOOK OF INVERTEBRATE ZOOLOGY.

descence of the living animal. If the cuticle is found
difficult to remove, it may be loosened by placing the
animal in warm water for a short time.

c. The hypodermis (Figs. 88, b, and 89) , or cellular layer
by which the cuticle is excreted. When examined with a
high power a thin section of a favorable specimen will
show that the stained protoplasm of this layer forms a
polygonal honeycomb-like structure of thin vertical plates,
and that the spaces between these plates are filled by a
transparent inter-cellular substance.

d. A layer of circular muscular fibres (Figs. 88, c,
and 89) lies just within the hypodermis. The pigment
which gives the dorsal surface of the body its dark color
is situated in this layer, in the form of minute dark granules
scattered among the muscular fibres.

e. A layer of longitudinal muscular fibres (Figs. 88, d,
and 89), which varies greatly in thickness in different parts
of the body. This layer is not perfectly continuous
around the entire circumference of the body, but is inter-
rupted along the line of the setae, so as to form eight lon-
gitudinal bands, four of them very narrow and the other
four wider.

1. The widest band (Figs. 88, e, and 89) covers the dorsal
surface and sides, and may be called the dorsal band. It
extends from the uppermost setae on one side to the cor-
responding setae on the other side.

2. The ventral band (Figs. 88, /, and 89) is much nar-
rower, and covers the ventral surface, between the lowest
setae.

3. A lateral band (Figs. 88, g, and 89) runs on each
side between the two pairs of setae.

4. There are two narrow bands (Figs. 88, /<, and 89) on
each side, between the two setae of each pair.

STRUCTURE OF THE EARTHWORM.

155

Co
FIG. 89.

FIG. 89. — Transverse section through the body of Lumbricus terrestris
near the middle of the intestine. (Slightly changed from Claparede. Taf.
xliv.. Fig. 2.)

156 HANDBOOK OF INVERTEBRATE ZOOLOGY.

FIG. 89. — a to h. As in Fig. 88. i. Cavity of intestine, j. Epithelium
of intestine, fc. Layer of circular muscular fibres around intestine.
I. Layer of longitudinal muscular fibres around intestine, in. Green layer
on outer surface of intestine, n. Dorsal vessel, o. "Liver."

f. Notice that the muscular fibres of this layer do not
form a thin stratum on the inner surface of the layer of
circular fibres, but are arranged in bundles or leaflets,
which project into the body cavity so as to form a series
of parallel ridges. Each ridge consists of a central plate,
with muscular fibres on each side of it ; and, in transverse
section, has somewhat the appearance of a feather. A
longitudinal section of the body-wall will show that the
circular muscles have a similar feather-like structure when
cut across.

g. The body cavity is lined by a vascular layer (Fig.
89, c) which covers the inner surface of the muscular bun-
dles, and is rich in small vessels.

7^. Covering these vessels and separating them from the
body cavity, the nuclei of a delicate layer of epithelial cells
may be made out in favorable specimens, with a high
power.

J3. The dissepiments between the somites. In a section
which contains the whole or a part of one of these parti-
tions, notice the muscular fibres, which consist of: —

a. A layer of circular fibres (Fig. 88, j) around the
digestive tract.

b. A second set of circular fibres (Fig. 88, &) around
the nervous system and ventral blood-vessel.

c. Fibres which radiate inwards from the body wall
towards the centre.

d. A few nearly vertical fibres which run from the dor-
sal to the ventral surface.

e. The surface of the partition is covered by an epithe-
lium, which is rather difficult to detect.

STRUCTURE OF THE EARTHWORM.

157

III. The Setae. In a section which contains setae, no-
tice : —

a. The complicated system of muscles running from the
inner end of the seta to the surrounding integument.

b. Small, partially developed setae near the inner end of
each large one.

c. The sheath around the outer end of the seta, formed
by a tubular infolding of the cuticle.

IV. The Nervous /System.

FIG. 90.

FIG. 90. — Transverse section through the ventral ganglia, near the
middle of the body. (From Claparede. Taf. xlvii., Fig. 4.)

a. Surface epithelium, b. Muscular layer. c. "Tubular fibres."
d. The two ganglia. /. Outer layer with large ganglion cells, g. Lateral
nerves, h. Ventral blood-vessel.

Examine with a high power, — two hundred and fifty to
five hundred diameters, — a section which passes through
one of the ganglionic enlargements of the ventral nerve
cord, and notice : —

a. The layer of epithelium (Fig. 90, a) which forms its
outer sheath.

158 HANDBOOK OF INVERTEBRATE ZOOLOGY.

6. A thick layer of longitudinal muscular fibres (Fig.
90, 6) between which numbers of small, nucleated cells
are scattered.

c. The tubular bands; three longitudinal bands (Fig.
90, c) which lie in the muscular layer, on the dorsal side
of the nerve cord.

d. The two ganglia (Fig. 89, d) which are imperfectly
separated from each other along the median line. Each
consists of : —

1. A layer of large, granular, nucleated ganglion cells
(Fig. 89,^) which lie upon its ventral surface and sides.

2. A central and dorsal non-transparent area (d) which
consists almost entirely of extremely fine intertwined
nerve fibres.

e. The nerves (Fig. 90, g] which run off on each side,
and consist of fine fibres like those in the dorsal portion
of the ganglion.

g. The blood-vessels ; especially the large ventral ves-
sel (h) which runs along the body below the nervous
system.

V. The Digestive Organs.

a. In a section which passes through the pharynx, no-
tice : —

1. The central cavity (?) which is reduced to a narrow
slit by the folding together of its walls. The form of this
slit varies greatly in sections from different parts of the
pharynx.

2. A delicate layer of transparent cuticle, which lines
the cavity.

3. -The epithelium, formed by a single layer of large
nucleated cells.

4. The very numerous blood-vessels, which lie just out-
side the layer of epithelium.

STRUCTURE OF THE EARTHWORM. 159

5. The greater part of the wall of the pharynx is made
up of a mass of muscular fibres, which are entwined in all
directions.

5. In a section through the oesophagus (Fig. 88), notice
that, —

1. The muscular wall is divided into an outer layer (o)
of longitudinal fibres, and an inner layer (p) of circular
fibres.

2. The epithelium (n) is thrown into folds or papillae,
and each contains a looped branch of a blood-vessel.

3. The cuticle (m) is more distinct than in the sections
of the pharynx.

c. In a section through the cesophageal glands notice that
these are simple pouches formed by pushing out the wall
of the ossophagus into the body cavity. The most ante-
rior pair contain the calcareous bodies noticed in Section
XV.

d. Sections through the crop and gizzard are much like
those through the oesophagus, except that the muscular
layer is much more developed.

e. In sections through the intestine (Fig. 89) notice the
very peculiar manner in which the dorsal wall (/*) is
pushed down towards the ventral, thus reducing the cav-
ity (i) to a narrow slit. Notice that the epithelium (j),
the vascular layer, the layer of circular muscular fibres (&),
and the layer of longitudinal muscular fibres (?) are ar-
ranged as in the oesophagus.

1. Outside the layer of longitudinal fibres notice a
thick layer (m) of granular greenish cells, which is re-
flected above onto the dorsal vessel (<?) and its branches,
thus forming the so-called liver (o).

160 HANDBOOK OF INVERTEBRATE ZOOLOGY.

XVII.— THE GENERAL ANATOMY OF THE LEECH.

Macrobdilla decora.

I. SPECIMENS for examination should be killed with chlo-
roform, and they may then be examined, or they may be
preserved in alcohol. If the large pond leech cannot be
procured, the medicinal leech may be used. Examining
a fresh or an alcoholic specimen, notice the following ex-
ternal characteristics.

a. The arched, dorsal surface of the long, ribbon-like
body. This surface is distinguished by its dark, olive-
green color, as well as by the regular arrangement of the
pigment spots.

b. The flattened, light-colored ventral surface, upon
which the pigment spots are very irregularly distributed.

c. The anterior end of the body may be recognized by
its protrusible proboscis, or sucker, which is formed by
the upper lip, and projects over the mouth.

d. The posterior end of the body terminates in a much
larger sucker, with an unbroken circular outline. The
disk of the posterior sucker is imperforated, and faces
ventrally.

e. On the dorsal surface, note :

1. The annuli or rings which encircle the body. These
are about one hundred in number, and must not be mis-
taken for the true somites into which the body is divided.

2. The proboscis is made up of four incomplete annuli,
and the first complete ring.

3. The ten black eyes, which are arranged in a horse-
shoe upon the dorsal surface of the anterior end of the
body.

GENERAL ANATOMY OF THE LEECH. 161

Two of these eyes are upon the first annulus.

Two upon the second.

Two upon the third.

Two upon the fifth.

Two upon the eighth.

It is probable that each pair of eyes corresponds to a
body somite. The first annulus must therefore be re-
garded as the first somite ; the second annulus as the
second somite ; the thfrd and fourth annuli as the third
somite ; and the fifth, sixth, and seventh annuli as the
fourth somite.

4. The two rows of black pigment spots along the
edges of the body.

5. A median dorsal row of light-colored spots. Each
somite posterior to the fourth is made up of four or five
annuli, and the pigment spots are on the first annulus of
each somite. The body is thus seen to be made up of
twenty-five somites, without counting the posterior sucker,
which is shown, by its mode of development, to consist
of seven somites.

6. On the dorsal surface in the groove which separates
the most posterior annulus from the sucker, notice the
anus.

7. Make a drawing of the dorsal surface, to show these
points.

f. On the ventral surface, notice : —

1 . The mouth , bounded anteriorly and ventrally by the
proboscis, and ventrally by the ventral portion of the
fourth annulus.

2. A thickening of the median ventral portion of the
thirtieth annulus, in the centre of which the male repro-
ductive o)-(/(ni is placed. In specimens which have been
killed with chloroform, the penis usually projects a little
from the opening.

162 ' HANDBOOK OF INVERTEBRATE ZOOLOGY.

3. The female reproductive orifice is on the median
line, between the thirty-third and thirty-fourth annuli.

4. A nearly square region, formed by the thickening
of the ventral portions of the thirty -ninth, fortieth, and
forty-first annuli, and pierced by two pairs of fine pores,
the external openings of the mucous glands.

5. The external apertures of the segmented organs,
With a hand-lens two small papillae may be seen pro-
jecting backwards from the posterior margin of every
fifth annulus; one on each side, near the edges of the
ventral surface. The openings are upon the posterior
annulus of each somite, that is, the annulus just in front
of the one which has a pigment spot upon its dorsal
surface.

6. Make a drawing of the ventral surface, to show all
these points.

II. Internal Structure.

Specimens for dissection may be killed with chloroform,
and preserved in seventy-five per cent alcohol. A day
or two before they are to be dissected, they should be
placed in water, to soften them.

Cut through the integument, along the middle of the
dorsal surface, from the second or third annulus to the
last but one. With a pair of fine forceps lift up one edge
of the integument, near the middle of the bod}-, and Avith
a pair of fine-pointed scissors cut the blood-vessels, mus-
cles, and connective tissue which bind it to the upper sur-
face of the digestive tract. Pin the flap of skin down
on to a flat piece of cork or a wax tablet, under water,
and then free the opposite edge, and pin it out in the
same way. Work forwards and backwards from these
two pins, pinning down the integument at short interval-.
If this is carefully done, the whole digestive tract will
now be exposed in place.

GENERAL ANATOMY OF THE LEECH. 163

a. The digestive tract consists of a buccal pouch, a
pharynx, a stomach, and an intestine. The buccal pouch
may be examined later. In the other parts, notice : —

1. The muscular, thick-walled, tubular pharynx, which
forms about the first tenth of the total length of the di-
gestive tract. It is bound, by radiating muscular fibres,
to the body wall.

It is much larger in the middle than at the ends, where
the wall contains circular muscles, which may by their
contraction entirely close the tube.

3. The " stomach " is a large sacculated pouch, which
joins the pharynx abruptly, and nearly fills the body cav-
ity. Its walls are much thinner than those of the pha-
rynx, and are only very slightly muscular. It occupies
about five-sixths of the total length of the body, and is
divided, by deep constrictions which run nearly to the
middle line, into eleven pouches or chambers, each of
which, except the last, fills the body cavity of one somite,
while the constrictions which separate the pouches cor-
respond to the partitions between the somites. These
partitions may be seen to run into the spaces between the
pouches, so as to form imperfect dissepiments between the
cavities of adjacent somites.

The cavity of the stomach is made up : —

(i.) Of a central tube, which is continuous with the
pharynx along the middle of the body, and is greatly con-
stricted at each dissepiment.

(ii.) Of the cavities of the sacculi upon each side of
this central tube.

The squeezing to which the blood is subjected in this
" stomach," in order to separate the fluid from the solid
portions, is effected by the pressure of the outer wall of
the body, only slightly aided by the muscles of the stom-
ach itself.

164 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(iii.) The posterior end of the " stomach " forms a small
papilla which projects into the " intestine."

4. The "intestine" enlarges a little, near its anterior
end, and then tapers gradually to the anus.

5. Make a sketch of the digestive tract, showing these
points.

b. Cut through the middle of the dorsal wall of the
digestive tract, with a pair of scissors, in order to expose
the interior. Wash out, with a stream of water, any food
which may remain in the stomach ; and, examining the
various regions with a lens, notice : —

1. The pharynx. Its walls are very thick and mus-
cular, and are joined to the integument by radiating mus-
cles, which, by distending its cavity, produce a sucking
action.

2. The cavity is largest in the middle, and opens into
the stomach through a small round aperture surrounded by
muscles.

3. Six or eight large longitudinal bundles of muscles
give to the inner wall of the pharynx a plicated appear-
ance. By the action of these muscles the blood which has
been sucked into the pharynx by the contraction of the
radiating muscles, is driven backward into the sacculi of
the stomach.

4. Each sacculus is divided, on each side the middle line,
into an anterior and a posterior chamber. The posterior
chamber is the larger, and is prolonged downwards and
backwards.

5. The posterior chambers of the last or eleventh saccu-
lus are much larger than the others, and run backwards to
form two large horn-like diverticula, which reach nearly
to the posterior end of the body.

6. Between the anterior ends of these diverticula the

GENERAL ANATOMY OF THE LEECH. 165

" intestine " originates, and runs backwards on the median
line of the body. It is much smaller than the " stomach,"
tubular and muscular.

7. Near its posterior end the intestine dilates to form an
ovoidal colon.

8. From this a very small and short rectum runs to the
dorsal anus, which lies between the last annulus and the
sucker.

c. Cut the digestive tract at the anus, and at about the
middle of the pharynx, and carefully dissect it away and
remove it, to expose the organs "which lie below. On the
inner surface of the ventral body- wall, notice : —

1. The median ventral nerve-cord, made up of: —

(i.) A series of ganglia; one in each of the somites
except those at the anterior end of the body. These
ganglia give rise to lateral nerves which may be traced out
into the body-wall.

(ii.) The commissures which join these ganglia into a
chain.

2. The ventral blood-vessel, a transparent tube which
surrounds the nervous system, and sends off lateral
branches.

3. The two lateral blood-vessels, running along the
sides of the body.

4. The segmental organs ; a row of eighteen pairs of
convoluted tubular organs, one for each somite of the body,
situated just inside the lateral vessels. Each of these
is connected with a transparent membraneous globular
vesicle.

5. The male reproductive organs.

(i.) About one-sixth of the length of the body from the
anterior end the globular muscular penis will be seen. It
is prolonged into a siphon-shaped tube, which opens exter-

166 HANDBOOK OF INVERTEBRATE ZOOLOGY.

nally upon the median line, a little behind the globular
portion.

(ii.) Two convoluted white glandular bodies, the vesi-
cula seminales, are situated a little anterior to, but in
the same somite with, the penis. They open into this at
one end, and at the other they connect with —

(iii.) The testes, nine pairs of small white glandular
bodies situated close to the nerve cord. The lirst pair are
in the fourth somite behind that which contains the penis,
and the others are in the eight following somites, a little in
front of the segmental organs.

6. The female reproductive organs. These are in the
somite next behind that which contains the penis, and are
made up of: —

(i.) The vagina; a muscular sac upon the median
line.

(ii.) The twisted oviduct running from the top of the
vagina. It soon divides into two branches which run
down towards the ventral surface, and terminate in the
small white ovaries.

7. In the segment next behind that which contains the
female organs, notice the two pairs of white convoluted
mucous glands.

8. Make a sketch showing the reproductive organs in
place.

9. The nervous system. This consists of: —

(i.) A double commissural cord, which runs from one
end of the body to the other, and consists of two fibres
which lie side by side in a common sheath for the greater
part of their length.

(ii.) The series of twenty-one ganglia.

(a.) The first of these is the largest, and gives off five
pairs of nerve-.

GENERAL ANATOMY OF THE LEECH. 167

(b.) The remaining ganglia, except the two last, give
off two nerves each on each side.

(c.) The most posterior ganglion but one gives rise to
only one pair of nerves.

(d.) The last ganglion is much larger than those which
immediately precede it, and gives off seven pairs of nerves.

(iii.) Anterior to the first ventral ganglion the two
commissural fibres diverge from each other and bend up
around the anterior end of the pharynx to form the mouth-
ring. On the upper surface of the anterior end of the
pharynx they end in, —

(iv.) The supra-cesophageal ganglion, or brain, com-
posed of two halves meeting in the median line.

(«.) Each half of the brain gives rise to five optic
nerves, which pass to the eye-spots of that side of the body.

(b.) The brain is also united to the three stomato-gastric
or sympathetic ganglia ; one on each of the three muscu-
lar lobes of the buccal pouch. One of these ganglia lies
in the median line in front of the brain, and is united at
each end to one-half the latter. The other two are upon
the sides, and each joins the corresponding half of the
brain.

III. The Mouth. This may now be examined in the
dissected specimen. By bending up the upper lip the tri-
angular opening of the mouth may be seen at the bottom of
the cavity of the anterior sucker. The ventral slit is verti-
cal, and the two dorsal slits are inclined towards it so as to
form a Y. Open the buccal cavity by a cut along one of
the slits, and notice the three large white buccal muscles
which occupy the spaces between these grooves or channels,
of which the three slits are the external ends. In the
medicinal leech the teeth are placed upon the inner surfaces
of these muscles.

168 HANDBOOK OF INVERTEBRATE ZOOLOGY.

XVIII.— THE STUDY OF THE HARD PARTS OF
THE COMMON CRAB.

(Callinectes hastatus.)

A STUDENT of the elements of Morphology can hardly
grasp the significance of the structure of the Decapod
Crustacea until he has studied several forms, and as excel-
lent directions for studying the crayfish or lobster are
within the reach of most students, it seemed best to de-
scribe some other type here. If the student has verified
the description of the crayfish or lobster which is given
by Huxley, Packard, or Huxley and Martin, the study
of a crab will serve as a review, and will throw new light
upon the significance of the facts. For the benefit of
those students who have not gone over this ground, I shall
give, in the next section, a brief description of the hard
parts of the lobster, and a lobster or a crayfish should, if
possible, l)e examined at the same time that the crab is
studied.

If squilla can be procured, it should also be examined
at the same time, but as it is not readily procurable, I give
no description of it.

The common edible crab may be found in abundance in
all the inlets, bays, and sounds of our southern coast;
and as it may also be obtained, during the winter, in the
markets of our larger cities, it is a good form to select for
laboratory work. If it cannot be procured, any other
crab will answer nearly as well, and most of the points
may be verified in the common shore crab (Cancer irrora-
tus) of the Xew England coast. This latter crab may be
collected in the crevices of rocks near low tide mark, and

HARD PARTS OF THE COMMON CRAB. 169

it may be preserved in alcohol, or studied while fresh. If
specimens are to be preserved for winter work, they
should be bled before they are placed in alcohol. This is
done by puncturing the soft integument of the dorsal sur-
face between the posterior edge of the carapace and the
first abdominal somite. They should then be placed in
eighty or eighty-five per cent alcohol, which should be
renewed in four or five days. Specimens for studying
the hard parts may be dried in the sun.

I. The Dorsal Surface.

The dorsal surface of the body is almost entirely cov-
ered by the carapace, which, in Callinectes, is about three
times as wide as it is long ; irregularly rhomboidal, with
its outer angles prolonged into two sharp-pointed, pro-
jecting horns. Observe : —

a. The anterior, nearly semicircular, serrated margin.

1. The middle of this margin is marked by a concave
notch, beneath which a short spine projects from the
middle line of the body. The spine does not form part
of the carapace, but is attached to the ventral or sternal
portion of the antennary somite.

2. On each side of the spine notice that the antennules
project beyond the overhanging edge of the carapace.

3. Outside these, on the edge of the carapace, the me-
dian pair of serrations. ( This pair of serrations, together
with the notch between them, represent the protruding
rostrum of the lobster or the crayfish.

4. The next pair of serrations are rounded, and over-
hang the antennae, and outside them, on each side, is an
area, free from teeth, below which is the eye.

5. The edge of the carapace, between this space and the
outer angle, is occupied by eight serrations, which are
nearly alike in size and shape.

170 HANDBOOK OF INVERTEBRATE ZOOLOGY.

b. The posterior margin of the carapace is divided into
a median and two lateral portions. It carries no large
serrations, but a very finely dentated ridge runs parallel
to and very near its edge.

c. The dorsal surface of the carapace is mapped out by
depressions into several areas.

1. On the dorsal median line, somewhat nearer the pos-
terior than the anterior end, there is a transverse depres-
sion, about half an inch long, the outer ends of which
unite, at an obtuse angle, with two straight depressions,
which run forwards and outwards, to unite anteriorly with
two lines which run outwards on to the horns at the lateral
angles of the carapace.

This system of depressions appears to be homologous
with the cervical suture of the crayfish or lobster, and
divides the carapace into an anterior cephalic, and a poste-
rior thoracic area.

(i.) The thoracic area is again divided, by a pair of
faintly marked depressions, running from the outer ends
of the transverse bar of the cervical suture to the edges
of the carapace, over the last pair of legs, into a central
cardiac, and twro lateral branchial areas.

(ii.) The cephalic area is divided into the following
regions :

(«.) An irregular transverse depression, crossing the
middle of the carapace near its anterior edge, and bend-
ing forward at its ends to meet the anterior edge over the
eyes, marks of an anterior or facial region, which is again
divided into a nunY\un frontal lobe, and two orbital lobes.

(6.) The space between the facial depression and the
cervical suture is divided by two longitudinal furrows into
a large, median, sub-triangular, gastric region, and two
hepatic lobes.

HARD TARTS OF THE COMMON CRAB. 171

The hepatic lobes are bounded externally by the ser-
rated anterior margin of the carapace, posteriorly by the
cervical suture, and internally by the gastric area and
optic lobes.

(c.) Posterior to the carapace, the dorsal or tergal sur-
face of the tirst abdominal ring or somite is visible in a
dorsal view.

d. Make a sketch of the dorsal aspect, showing all these
points.

II. The Ventral Surface.

On the median line of the posterior portion of the ven-
tral surface, notice the abdomen (Fig. 91, a.b), which is
bent downwards and forwards, so that its ventral surface
faces upwards, and is in contact with the ventral wall of
the thorax, while its dorsal surface faces downwards, and
is external. The abdomen fits into a groove or depression
in the ventral wall or xternal plastron of the thorax, and
presents considerable sexual variation.

a. In the male (Figs. 91 and 103, ab), it is narrow
and wedge-shaped, and fits closely into its groove. Raise
it up with the handle of a scalpel, and notice the two
teeth by which it is locked into place.

It. The abdomen of the female (Fig. 102, «&), is
broad and rounded, and its inner or ventral surface is
concave, thus forming a broad chamber for containing and
protecting the developing eggs. It consists, in the female,
of six flattened) movable rings, or somites, which are cal-
cified and hard upon their exposed or dorsal surfaces, and
soft and membraneous on their internal or ventral surfaces.

1. The first, second, third, and fourth abdominal somites
of the female carry paired appendages, the pleopods (Fig.
102, pi). Each appendage is fringed with long hairs, to
which, during the breeding season, the eggs are fastened,
and consists of : —

HARD PARTS OF THE COMMON CRAB. 173

FIG. 91. — Ventral surface of male specimen of Callinectes hastatus.
(Drawn from nature by W. K. Brooks.]

ab. Abdomen. 6. Basipodite. c. Carpopodite. ex. Coxopodite.
d. Dactylopodite. ep. Episterna. is. Ischiopodite. m. Meropodite.
mps. Third niaxillipeds. s"1 — sviii. Sterna of thorax. pl — p5. The five
pairs of pereiopods. p. Propodite.

(i.) An oblong basal joint, or protopodite, which runs
backwards and forwards, and carries two long, slender,
terminal filaments.

(ii.) The inner one of these, the endopodite, is attached
to the inner margin of the protopodite close to its distal
end.

(iii. ) The outer one, or exopodite, is attached to the outer
margin of the protopodite near its proximal end.

2. Straighten out the abdomen of the female, and notice
that its dorsal or external surface is continuous with the
carapace, while its soft, internal surface is continuous with
the ventral surface of the body. Separate the second
abdominal somite, and having cleaned out the soft parts,
examine it from one end, and notice : —

(i.) The broad, hard, slightly-arched, dorsal surface, or
tergum.

(ii. ) The two lateral flaps, or pleura, which project from
the sides of the tergum, beyond the outline of the ventral
surface.

(iii.) The soft, membraneous, ventral portion, or ster-
num, much shorter from side to side than the tergum.
Notice the point where the appendage is attached, between
the tergum and the sternum. The sternum is usually
regarded as consisting of three portions, a median true
sternum, with an epistemum on each side, between the
true sternum and the base of the limb, but no such divis-
ion can be seen in the sternum of the abdominal somite
of a crab.

174 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(iv.) The portion of soft integument which lies between
the joint of the appendage and the terguin is the epime-
ron. This can hardly be recognized in the abdomen of
the crab.

c. The male abdomen (Figs. 91 and 103, a&), is made
u]) of four pieces. The first corresponds to the first in
the female abdomen ; the second is formed by the fusion
of the second, third, and fourth rings : while the third
corresponds to the fifth in the female, and the fourth to
the sixth.

d. The male abdomen carries only two pairs of append-
ages, modified to form copulatory organs.

e. In both sexes, the anus is placed upon the sternal
surface of the last abdominal somite.

f. Make sketches of the male and the female abdomen,
showing these points.

g. The Sternal Plastron.

This is the broad, shield-shaped ventral skeleton of that
portion of the body which lies between the basal joints of
the five pairs of legs. Its surface is excavated in the
middle line for the reception of the abdomen. It is made
up of the united sterna and episterna of a number of
somites.*

1. On its exposed surface notice five distinct sutures or
folds ; the lines of union between the posterior six of the
eight sterna (Fig. 91, sl-svm), which enter into it.

2. Wedged in between the outer ends of these sterna,
"notice the episterna of the corresponding somites ; each

* As the critical discussion of disputed points would be out of place
in this work, I have followed Milne Edwards in this description. His
terminology is the one which the student will meet in text-books mid
lectures, and it does not seem advisable to create confusion by changes,
which, to the beginner, would seem arbitrary and meaningless.

HARD PARTS OF THE COMMON CRAB.

175

episternum (Fig. 91, jp), being anterior to the outer
end of its own sternum, and articulating with the basal
joint of an appendage.

h. The Appendages.

Six pairs of appendages, the third pair of Maxillipeds
(Fig. 91, m p3), and five pairs of legs, or pereiopods,
(pl,p2, p3,p4, p5}, are articulated around the lateral and
anterior margins of the sternal plastron.

1. The third maxillipeds (Fig. 91, mp3, and Fig. 92),
meet upon the median line in front of the anterior angle
of the sternal plastron, and they are flattened so as to
form a square operculum, which covers the more anterior
mouth parts.

Flo. 02.

FIG. 92. — Outer surface of left third maxllliped of Callinectes hasta-
tus; natural size. (Drawn from nature by W. K. Brooks.)

p. Protopodite. en. Endopodite. ex. Exopodite. /. Flabellum.

b. Basipodite. ex. Coxopodite. is. Ischiopodite. m. Meropodite.

c. Carpopodite. pr. Propodite. d. I)actylopodite.

Like the abdominal appendage, or pleopod, this ap-
pendage is divisible into three regions, a protopodite (Fig.
92, p), an exopodite (Fig. 92, ex), and an endopodite
(Fig. 92, en), but each of these regions is again divided
into parts.

176 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(i.) The protopodite (p) is obscurely divided into two
joints. The proximal one, articulating with the sternal
plastron, is known as the coxopodite (c) and the distal one
as the basipodite (b). The protopodite carries, besides the
exopodite and the endopodite, a long, hairy process, the
flabellum, or epipodite (Fig. 92, f). In order to expose
the flabellum, the appendage must be removed from the
body.

(ii.) The exopodite, (Fig. 92, ex], is long and slender,
and divided into two portions, the distal one being ob-
scurely many-jointed.

(iii.) The endopodite (Fig. 92, en), is divided into two
regions, a proximal, greatly flattened, two-jointed region,
or gnathostegite, and a terminal, three-jointed, slender,
finger-like process, the endogna thai palp.

(iv.) The large, flattened, basal joint of the gnathoste-
gite (Fig. 92, is), is the ischiopodite, and the smaller
terminal joint (m) is the meropodite.

(v.) The basal joint (c) of the endognathal palp, is the
carpopodite; the middle joint (pr) the propodite, and
the terminal joint (d) the dactylopodite.

2. The Pereiopods.

The five pairs of leg?, or pereiopods, are quite similar
in structure. Each consists of a two-jointed protopodite,
and a long, five-jointed limb, or endopodite ; the exopo-
dite being absent. The seven joints which make up the
limb are then the basipodite (Fig. 91,j?) [see foot-note
on p. 174], coxopodite (ex), ischiopodite (is), meropo-
dite (m), carpopodite (c), propodite (p), and dactylopo-
dite (d). The joint between the second and third por-
tions, the ischiopodite, and coxopodite, admits of very little
motion, and the two pieces are almost fused with each
other. '

HARD PARTS OF THE COMMON CRAB. 177

(i.) The first pereiopod is much larger and stronger than
any of the others, with serrations along its anterior edge,
and the tip is colored bright blue in the male, and red in
the female. The distal end of the propodite is prolonged
forwards as a finger-like process, which, lying parallel to
the dactylopodite, forms the chela, or claw. The opposed
edges of the halves of the claw are set with tooth-like
serrations, and these are round and blunt in one claw,
sharp and pointed in the other.

(ii.) The second, third, and fourth pereiopods are
very like each other, shorter than the first, and without
chelse.

( iii. ) The fifth pereiopod has its terminal joints flattened,
and fringed with hairs, and is a paddle-shaped swimming
organ.

(iv. ) On the inner ventral edge of the coxopodite of the
fifth pereiopod of the male, notice a delicate membraneous
tube, the projecting tip of the vas deferens. It passes
into the base of the first abdominal appendage.

i. The female reproductive orifices are covered by the
abdomen, and are near the middle line on the sternum of
the somite which carries the third pair of pereiopods.

j. In front of the coxopodite of the first pereiopod,
notice a large aperture through which the water passes to
the gills. Move the third maxilliped, and notice that its
flabellum runs backwards and outwards from the protopo-
dite into this cavity.

k. Outside and anterior to the bases of the appendages,
the outline of the body is completed by the reflected ven-
tral portion of the carapace, on the anterior margin of
which are the eyes, the antennules, and the antennae.

I. Make a drawing of the ventral aspect, showing all
these points.

178

HANDBOOK OF INVERTEBRATE ZOOLOGY.

III. The Appendages.

Having removed the abdomen, carefully disarticulate
its appendages, and the five pairs of pereiopods, and lay
them aside in order, for subsequent examination. Raise
up and disarticulate the third maxillipeds, and carefully
remove them, with their long flabella.

a. Under thesfe notice the second and first pairs of max-
illipeds, much like the third pair, but more soft and mem-
braneous. Disarticulate the second maxilliped, and re-
moving it for examination, notice that it consists, like the
third maxilliped, of: —

(i.) A two-jointed proto-
podite (Fig. 93, p), which
carries two gills (^), and an
epipodite, or flabellum (f).

FIG. 93. — Outer surface of left
second maxilliped; natural size.
(Drawn from nature by W. K.
Brooks. )

y, (j. Gills. Other letters as in
Fig. 92.

(ii). A long, slender exopodite (ex), much like that of
the third maxilliped.

(iii.) A five-jointed endopodite (en), which is not flat-
tened to form an operculum, as in the third pair.

b. Remove the first maxillipeds, and examining them,
notice that, while they have a close resemblance to the
others, they are soft and foliaceous (Fig. 94), and with-
out gills. The flabellum (/) and exopodite (ex) are
much like those of the second and third maxillipeds, but
the two joints of the protopodite, the basipodite (b) and the
coxopodite (ex) are greatly enlarged to form two hairy
jaws, on each side, while the endopodite (en) is unjointed,
soft, membraneous, and fused with the exopodite.

FIG. 93.

HARD PARTS OF THE COMMON CRAB.

179

c. Notice now on each side of the rectangular mouth
area, orperistome, a large orilice which communicates with
a capacious chamber under the carapace.

This chamber is the branchial chamber, and the aperture
is that through which the water passes from the gills.
Lying in the mouth of this aperture, notice a thin, mem-
braneous, spoon-shaped scoop, the Scaphognathite, by the
movement of which,
during life, the water
is bailed out of the
branchial chamber.

FIG. 94. — Outer sur-
face of left first maxilli-
ped ; natural size. (Drawn
from nature by W. K.
Brooks. )

Letters as in Fig. 92.

FIG. 94

d. Raise up the edge of this scoop, and notice that it is
part of a thin, membraneous
appendage, the second maxilla

FIG. 95. — Outer surface of second
maxilla; natural size. (Drawn from
nature by W. K. Brooks. )
FIG. 95. sc. Scaphognathite. Other letters as

in Fig. 92.

Remove this appendage for examination, and notice that
the two divisions of the protopodite (b) and (ex) are
elongated, bilobed, and hairy. The lobes of the basipo-
dite (b) are long and slender, while those of the coxopo-
dite are more rounded. Outside these notice a short,
pointed, hairy process fen), which is the rudimentary

180

HANDBOOK OF INVERTEBRATE ZOOLOGY.

endopodite. The remainder of the appendage forms the
flattened scaphognathite (.sc), which is, probably, a modi-
fied exopodite.

e. After removing the second maxillae, notice under
them the still more delicate and foliaceous first maxilla?
(Fig. 96). Remove these, and notice that the basipo-
dite (b) and the coxopodite (ex) are very much elongated
and jaw-like, while the exopodite is absent, and the endo-
podite (en) is very small, but not quite as
eri rudimentary as that of the second maxilla.

FIG. 96. — Outer surface of left first maxilla;
natural size. (Drawn from nature by W. K.
Brooks. )

Letters as in Fig. 92.

C3-

FIG. 96.

f. Notice the cutting edges of the mandibles, which
meet each other on the middle line. Force them apart,
and notice between them the mouth, with its membrane-
ous, hairy upper lip, with several small calcifications, and
just posterior to the cutting edges of the mandibles notice
on each side of the middle line of the body a spatulate
process which runs downwards and lies in contact with the
surface of the mandible. These two processes form the
metastoma, or lower lip. Each
consists of a calcified rim or
frame, covered by a soft mem-
brane.

FIG. 97. — Outer surface of left man-
dible; natural size. (Drawn from na-
ture by W. K. Brooks. )

a, a. Apodemata. b. Body of Man-
dible, p. Mandibular palpus.

Fie. 07.

Remove the mandibles, and, examining them, notice that

HARD PARTS OF THE COMMON CRAB. 181

each consists of a dense, solid body (6) , and a movable,
two-jointed portion (/?). The body is the basal joint or
basipodite, which is greatly thickened and elongated, and
which carries a stout, cutting blade upon its inner end.
The two-jointed portion (p) is the mandibular palp. It
bears a general resemblance to the endopodite of an ordi-
nary appendage, but its mode of development, which will
be noticed later, has induced most authorities to regard it
as without an homologue in a typical appendage, and ac-
cording to this view the mandibular endopodite is absent,
as well as the exopodite. Near the ends of the mandible
notice two plates, or apodemata, which run inwards, and
furnish attachment for the mandibular muscles.

g. The remaining appendages are arranged in a longi-
tudinal row along the anterior margin of the carapace ;
the antennules in the centre, the eyes on the outside, and
the antennae between the eyes and the antennules.

1. The antenna (Fig. 98) consists of an enlarged, ir-
regular basal joint (a), which is so firmly fastened to the
shell that it admits of hardly any motion, and which
carries a hairy spine (b) ; and a slender terminal portion,
or flagellum (c) , which consists of two long basal joints,
and a great number of short rings.

FIG. 98. — Outer surface of left antenna of Callinectes
hastatus; natural size. (Drawn from nature by W. K.
Brooks. )

a. Basal joint, b. Spine, c. Flagellum.

FIG. 99. — Outer surface of left antennule of
Callineetes hastatus; natural size. (Drawn from na-
ture by W. K. Brooks. ) <

a. Basal joint, b. Shaft, c. Flagella. FIG. 99.

Carefully disarticulate the antennae, and place them
with the other appendages.

182 HANDBOOK OF INVERTEBRATE ZOOLOGY.

2. The antennules (Fig. 99) consist of a largo, hairy,
basal joint (a), which is freely movable, and which carries
a large, two-jointed shaft (6), which ends in two small,
many-jointed flagella (c) .

Carefully disjoint the antennules, and examining the
inner surface of the basal joint, notice a longitudinal slit,
covered with hairs, and completely closed. This slit
marks the position of the external opening of the ear in
the young. In the adult crab it is closed, although it
remains permanently open in the lobster or crayfish.

3. Outside the antennae are the large, movable, stalked,
compound eyes. Raise them up and disjoint them, and
place them with the other appendages.

h. Study and compare the appendages. Each pair of
appendages is carried by a region of the body which
may, in certain Crustacea, be represented by a distinct
ring or somite, and a crustacean is therefore regarded
as consisting of as many somites as there are pairs of ap-
pendages.

The series of somites and appendages is therefore as
follows : —

1. Occular segment. Eyes. (This is not the proper
place for an examination of the question whether the eyes
are or are not homologous with the other appendages. I
have here followed the older writers, but not without
careful revision of the subject.)

2. Antennulary somite. Antennules. Auditory Or-

gans.

3. Antennary somite. Antennae.

4. Mandibular somite. Mandibles.'

5. Metastoma.

6. First maxillae.

7. Second maxillae.

HARD PARTS OF THE COMMON CRAB. 183

•

8. First maxillipeds.

9. Second maxillipeds.

10. Third maxillipeds.

11. First pereiopods, chelate.

12. Second pereiopods.

13. Third pereiopods. The oviducts open upon the

sternal portion of this somite.

14. Fourth pereiopods.

15. Fifth pereiopods, swimming organs, with male re-

productive orifices on their basal joints.

16. First abdominal somite. First pleopods.

17. Second Second pleopods.

18. Third " " Third pleopods, absent

in male.

19. Fourth K Fourth pleopods, absent

in male.

20. Fifth " " Appendages absent.

21. Sixth

i. Draw the appendages, in their natural order.

IV. On the ventral surface of the specimen from which
the appendages have been removed, notice that the car-
apace is reflected inwards along the sides, as far as the
bases of the legs, so that the opening by which water
passes under the carapace to the gills is a small, crescent-
shaped slit in front of the first pereiopod. Anterior to
the 'pereiopods, the lower surface of the carapace forms
the straight, longitudinal borders of the peristome.

The anterior border of the peristome is formed by the
antennary sternum, or epistoma, \vhich carries a projecting
median spine, and is joined to the overhanging edge of the
carapace by the median rostral septum.

V. The sternal plastron may now be removed, and
cleaned for examination.

184 HANDBOOK OF INVERTEBRATE ZOOLOGY.

a. On its dorsal surface notice the eight pairs of lami-
nated, pyramidal gills. The first pair are small and hori-
zontal, while all the others are vertical. The first and
second pairs are attached to the bases of the second max-
illipeds. The third pair lie over the bases of the third
maxillipeds, and the remaining five pairs lie above the
bases of the five pairs of pereiopods. Notice that each
gill consists of a series of plates or leaflets, connected by
an external tube, the vessel which carries venous blood to
the gills, and an internal tube, the vessel which carries the
aerated blood away from the gills. Remove the gills, and
clean out the muscles which fill the dee}), honeycomb-like
cells of the sternal plastron.

b. This is now seen to be a complicated hollow box,
divided, by great numbers of partitions, into irregular
cells. It is made up of the sternal, episternal, and epim-
eral portions of the somites which carry the appendages
between the first pair of maxillipeds and the last pair of
pereiopods.

1. The united sterna form the smooth, external surface.

2. The outer or ventral ends of the episfci-nti are visible
externally, wedged in between the outer ends of the
sterna. They are continued upwards towards the dorsal
surface as thin plates between the muscle chambers of
adjacent somites.

3. The united epimera form the sloping dorsal surface.
tbeflancs, upon which the gills rest, and they also send
plates down to complete the partitions between the muscle
cells.

4. Make sketches of the ventral and lateral aspects of
the sternal plastron.

VI. Clean the carapace, and, on the inner surface of the
anterior edge notice the attachment of the eyes, ant en-

HARD PARTS OF THE CRAYFISH OR LOBSTER. 185

nules, and antennae. In this view, it is plain that the eyes
are the first, or most dorsal pair of appendages, the an-
tennules next, and the antennae third. This arrangement
is obscured, on the outer surface, by the great size of the
eyes, in accordance with which these appendages have
pushed the second and third pairs towards the middle line
of the body.

XIX. — THE HARD PARTS OF THE CRAYFISH OR

LOBSTER.*

I. THE body is divided into two well-marked regions, —
the anterior, unsegmented portion, or cephalofhorax, to the
lower surface of which the walking limbs are attached ;
and the more narrow, posterior portion, or abdomen,
which is divided into seven movable portions or joints.
In a view of the dorsal surface, notice : —

a. The groat shield-like plate, or carapace, which covers
the back and sides of the cephalothorax.

b. The groove, or cervical suture, which divides it into
an anterior and a posterior region.

c. The long spine, or rostrum, situated upon the median
line of the anterior margin of the carapace.

d. The stalked eyes, and long, many-jointed anten-
nules and antenna' , which project from below the anterior
margin of the carapace, on each side of the rostrum.

e. The live pairs of long, jointed, walking limbs, which
project from below the sides of the carapace.

/'. The dorsal surfaces, or terga, of the segments of the
abdomen.

1. The first, second, third, fourth, fifth, and sixth of

* This section is copied, with slight changes, from "Biology," by
Huxley and Martin.

186 HANDBOOK OF INVERTEBRATE ZOOLOGY.

these are substantially alike, and consist of an anterior,
smooth, highly-polished portion, which is overlapped by
the posterior margin of the preceding segment, and a
rougher, posterior portion, the posterior margin of which
projects over the anterior margin of the succeeding seg-
ment.

2. The seventh, or terminal joint of the abdomen, the
telson, is a flattened, somewhat triangular plate.

3. At the sides of the telson are the paddle-shaped
swimmerets, the appendages of the sixth abdominal seg-
ment.

g. Make a sketch of the dorsal surface, showing all
these points.

II. The ventral surface.

a. Notice the lateral edges of the carapace, the rostrum,
eyes, antennules, and antennae, as before.

b. Back of these, the complicated mouth parts, meeting
each other on the median line.

c. Push these apart, and notice between them the aper-
ture of the mouth.

d. Back of the mouth parts are the five pairs of walk-
ing legs.

e. Between the basal joints of cadi pair is a plate, the
sternum, or ventral portion of the segment, to which the
pair of limbs is attached. The sterna which correspond
to the first four pairs of limbs arc immovably united to
each other, while the fifth is slightly movable.

f. Along the outer edges of the ventral faces of the
abdominal segments are the thin, flat, swimming feet,
varying somewhat in number and form, according to
the sex.

g. The swimming feet of the sixth abdominal segment
are much larger than the others, and arc the swimmerets
which are visible in a dorsal view.

HARD PARTS OF THE CRAYFISH OR LOBSTER. 187

7^. The narrow sterna of the abdominal segments, be-
tween the bases of the swimming feet.

i. The anus, in the soft integument of the lower sur-
face of the telson.

k. Note that the sternal surface which carries the eyes,
antennules, and antennae, makes a sharp angle — the cra-
nial flexure — with the sterna of the remaining segments.

I. Make a sketch showing these points.

III. Removing the third abdominal segment, with its ap-
pendages, notice : —

a. The arched dorsal surface of the segment, the
tergum.

b. The flaps, or lateral walls, pleura of the tergum.
The posterior margin of each pleuron overlaps the smooth,
anterior margin of the succeeding pleuron.

c. The narrow sternum, forming that portion of the
ventral surface which lies between the appendages.

d. The flexible membrane which covers the space be-
tv/een the sterna of adjacent segments.

e. The point of union of the appendage with the seg-
ment.

f. The '/;////' m, or those portions of the ventral surface
which lie external to the points of attachment of the ap-
pendages. The epimera are very short, and pass almost
directly into the inner walls of the pleura.

g. The appendages or pleopods of the third abdominal
segment consist of : —

1. A short, two-jointed, basal portion, or protopodite,
consisting of a shorter proximal, and a longer distal piece.

2. Two flattened plates, an outer exopodite, and an inner
endojiodife, attached to the distal end of the protopodite.

h. Make a sketch of the segment, showing all these
points.

188 HANDBOOK OF INVERTEBRATE ZOOLOGY.

i. The fourth and fifth abdominal segments closely
resemble the third.

j. The appendages or swimmerets of the sixth abdomi-
nal segment are very large, and are made up of —

1. A protopodite, which consists of a single, short,
strong joint.

2. A wide exopodite, fringed with long hairs, and
divided into two portions by a transverse joint.

3. A triangular cndopodite, also fringed with long hairs.
k. Make a sketch of this appendage.

L The second abdominal segment of the female is much
like the third, and carries a pair of ordinary pleopods,
and the appendages of the first abdominal segment of the
female are rudimentary.

in. In the male, the protopodite and endopodite of the
appendage of the second abdominal segment are elongated
and rolled up so as to form an imperfect tube.

n. The first abdominal appendage of the male is a sin-
gle plate, rolled into a tube, and lying in the groove upon
the second appendage.

0. The terga of all the segments anterior to the first
abdominal, are represented, or at least replaced by, the
carapace, which is made up of a median dorsal area, and
two lateral folds, or branchiostef/ites, which lie above the
bases of the pereiopods. Raise up the margin of this
fold, and notice the branchial cavity which lies below it.
Carefully cut away the fold from one side of the body,
and notice the plume-like gills.

p. Examine and remove the remaining appendages
from one side of the body, in the order in which they are
described, and place them in their natural order for exam-
ination.

1. The walking legs, or pereiopods, are made up of

HARD PARTS OF THE CRAYFISH OR LOBSTER. 189

seven movable joints, working in different planes, so that
the limb, as a whole, can move in any direction.

2. The mouth parts ; the most posterior pair of mouth
parts — the third maxillipeds — cover those anterior to
them, and must be removed in order to expose the latter.

3. The third maxilliped consists of a basal, two-jointed
protopodite, and three terminal portions.

(i.) The epipodite, which is a long, curved plate, which
extends into the branchial chamber, and carries a gill,
(ii.) A long, slender, many-jointed exopodite.
(iii.) A thicker-jointed endopodite.

4. The second maxilliped is much like the first, but its
endopodite is less stout.

5. The first maxilliped ^ much more slender, and smaller ;
its endopodite is flattened and foliaceous ; and the epipo-
dite is a simple plate.

6. The two pairs of maxillae, and the mandibles, are so
much like those of the crab, that it is hardly necessary to
describe them.

7. After the mouth parts have been removed, notice the
mouth, and, projecting forward over it from its posterior
margin, the oval metastoma, covered with short, stiff hairs.

8. Anterior to the mouth, the large antennas, each of
which consists of: —

(i.) A two-jointed protopodite.
(ii.) A long, multi-articulate endopodite.
(iii.) A flattened, scale-like exopodite.
(iv.) On the lower surface of the basal joint of the proto-
podite, notice the opening of the antennary gland.

9. The much smaller antennulw; each of which is made
up of a pair of jointed filaments, mounted upon a long
protopodite.

10. On the flat upper surface of the protopodite notice

190 HANDBOOK OF INVERTEBRATE ZOOLOGY.

a row of hairs which cover a small slit, the opening of the
auditory organ.

11. The large eyes, mounted at the tips of movable
cylindrical eyestalks.

12. Make sketches of the series of appendages.

XX. THE GENERAL ANATOMY OF A CRAB.

(Callinectes hastatus.)

EITHER fresh or alcoholic specimens may be used for
dissection ; but if fresh specimens are used, the various
parts may be rendered more conspicuous by covering the
specimen with alcohol after it has been opened. All the
dissecting should be done under water or alcohol.

I. GENERAL 'ANATOMY.

Select if possible a large female specimen ; kill it by
bleeding ; and open it by carefully cutting away the dorsal
portion of the carapace, taking care to avoid injuring the
internal organs.

a. In the specimen thus opened notice the tough, dark-
colored skin, which lies just inside the shell and lines it.
Cut away this skin or turn it out and notice : —

b. The large transparent stomach (Fig. 100, e) which
occupies the middle of the anterior half of the cavity of
the shell. It is pear-shaped in surface-view, with its ante-
rior end broadest. . Notice that the outer ends of the
anterior border are prolonged into a pair of horn-like pro-
cesses, which are attached by muscular fibres to the inside
of the anterior edge of the carapace, behind the orbital
notches.

c. A pair of calcified rods, the pterocardiac ossicles
(Fig. 100, i) lie transversely across the dorsal surface of

192 HANDBOOK OF INVERTEBRATE ZOOLOGY.

FIG. 100. — A female specimen of Callinectes hastatus, with the cara-
pace removed, showing the viscera in place on the right side, but partially
dissected on the left side. ( Drawn from nature by \V. K. Brooks.)

a. Anterior gastric muscles. 6. Pterocardiac ossicle, c. Middle gas-
tric muscles, d. Ophthalmic artery, e. Stomach. /. Pyloric ossicle.
ft. Posterior gastric muscles, h. Ovary, i. Liver, k. Branchial cham-
ber. I, .Gills. m. Flabellum. n. Flancs. p. Heart, q. Intestinal
coecum. s. External mandibular muscles.

the stomach. They are on the inside of the stomach, but
their opacity renders them conspicuous in a surface view.

d. A "pyloric" ossicle (Fig. 100, f) lies in the dorsal
wall of the stomach, near its posterior end.

e. Notice the anterior gastric muscles (Fig. 100, a)
which run from the inner ends of the "cardiac" ossicles to
the anterior edge of the carapace.

f. The middle gastric muscles (Fig. 100, c), running
from the " cardiac " to the " pyloric " ossicle.

g. The posterior gastric muscles (Fig. 100, g) which run
outwards and upwards from the " pyloric " ossicles to the
gastric region of the carapace.

h. A little posterior to the ends of these muscles notice
the enlarged ends of the internal mandibular muscles,
which are also attached to the gastric region of the
carapace.

i. On the middle line of the body above the stomach
notice^the median, or ophthalmic urlcrij (Fig. 100, d).

j. Follow this backwards to about the middle of the body,
where it enters the pericardium, a slightly transparent
membraneous pouch, which lies upon the middle line,
under the cardiac region of the crrapace. If the animal
be not quite dead the slow pulsations of the heart may be
seen through the pericardium.

k. Posterior to the pericardium, on the middle line of
the body, there is a hollow, somewhat below the level

GENERAL ANATOMY OF A CRAB. 193

of the surrounding organs. This hollow usually contains,
in the female, a portion of the orange-yellow ovary
(Fig. 100, /*), and underneath this the tubular, trans-
parent, convoluted, intestinal coecum (Fig. 100, <?), which
consists of two portions, — a long, very small tube, which
is twisted into a compact ball, a little to the right of the
middle line, and a larger portion which is nearly straight,
and runs backwards on the left of the middle line, into
the first segments of the abdomen, where it opens into the
intestine.

/. Below the intestinal coecum, portions of the light
grayish-yellow liver may usually be seen ; and if the pos-
terior free ends of all these organs are gently raised up,
the transparent, straight intestine may be seen running
backwards into the abdomen on the middle line below
them.

m. These organs and the pericardium are bounded
laterally by elevations which reach nearly to the dorsal
carapace, and are encased in a hard, white, calcified shell.
They are known as theflancs (Fig. 100, n), and they con-
tain the muscles of the pereiopods. Their inner edges are
nearly vertical, and form the walls of the depression for
the heart and intestinal coecum, while their outer surfaces
slope gently downwards and outwards.

n. The outer sloping surface of each flanc is covered by
the tough, transparent chitinous wall (Fig. 100, &) of the
branchial chamber, through which the long, pyramidal
gills (Fig. 100, ?) are visible. Turning the specimen
over, introduce a small tube into the crescent-shaped
opening at the base of the third maxilliped, and blow air
through the tube into the opening. Turn the specimen
over again, and notice that the air has passed into the
branchial chamber, between the gills (I) and the roof (k).

194 HANDBOOK OF INVERTEBRATE ZOOLOGY.

The branchial chamber is thus shown to open externally,
and its manner of development shows that it is entirely
external to the body cavity, and is formed by an infolding
of the shell, and its transparent roof (k) will be found to
be continuous, at each edge, with the oiVlinary calcified
shell which covers the rest of the body. Notice that the
branchial chamber runs back onto the flancs for some dis-
tance beyond the most posterior gill, and that there is u
flat, muscular band along its edge.

o. The space between the stomach in front and inter-
nally, the pericardium posteriorly, and the flancs and
branchial chamber externally, is occupied by the orange
ovaries (Fig. 100, h), which run forwards and outwards
along the sides of the stomach, to the anterior margin of
the carapace, and then backwards and outwards, along the
carapace, as far as the bases of its large lateral horns.
The character and size of the ovary varies considerably
according to the season, and in the late summer months,
after nearly all the eggs have been laid, it is usually much
smaller than it is shown in the figure, which was drawn
from a specimen which was caught in the winter.

p. A branch (i) of the liver also takes nearly the same
course, and runs outwards along the side of the stomach
and the anterior edge of the carapace. It is below the
ovary, but as it is a little wider, the inner or free ends of
the lobules into which it is divided are visible between the
ovary and the bases of the gills.

q. Make a drawing showing all these organs, in place,
as seen in a surface view.

r. The heart. Cut open the pericardium and expose
the heart (p) in place. It is a white, fleshy, somewhat
hexagonal organ, which lies in the cavity of the pericar-
dium, to the walls of which it is loosely attached. Near

GENERAL ANATOMY OF A CRAB. 195

its anterior edge notice a pair of circular, transparent
depressions, each of which is crossed by a transverse slit
or opening into the heart. These slit-like openings are
the ostia, by which the blood passes from the cavity of the
pericardium into the heart, and the transparent semicircu-
lar flaps are valves, which allow the blood to flow into the
heart, but prevent it from passing back into the pericar-
dium. On the posterior edge of the heart notice two
more ostia, similar to those near the anterior border.

1. At the anterior external angles of the pericardium
notice the sinuses by which the blood from the gills enters
it, to pass into the heart.

2. Notice the ophthalmic artery (Fig. 100, cf) which runs
forwards from the middle line of the anterior border of the
heart.

3. On each side of this artery a hepatic artery (dis-
sected out on the left side of Fig. 100) passes through the .
mandibular muscle to the ovary, the liver and anterior edge
of the carapace, and the antenna.

4. A small abdominal artery, not shown in the figure,
runs backwards from underneath the posterior border of
the heart to the abdomen.

5. Turn the heart over and notice the large sternal ar-
tery which runs downwards and forwards from the abdomi-
nal artery, just as it leaves the heart.

s. Remove the ovary and the liver from one side of the
body, tracing the course of the hepatic artery, and notice
near the anterior edge of the floor of the body cavity, the
great external mandibular muscle (Fig. 100, s).

t. The Respiratory Organs. Cut through the roof of
the branchial chamber of one side, and raising it up, notice
that its upper inner edge is continuous with the skeleton
of the flancs, while its lower external edge is continuous

196 HANDBOOK OF INVERTEBRATE ZOOLOGY.

with the reflected lower edge of the carapace. Dissect the
membrane away and expose the gills.

1. Each gill is pyramidal in shape, and is made up of a
series of leaflets, which are bound together by a tubular
stem, the vessel which carries venous blood to the gills.

2. At the bottom of the gill-chamber notice a long, flat,
sword-shaped flap (w) fringed with hairs, — the flabellum
of the first maxilliped. Separate the mouth-parts, and
seizing the base of the first maxilliped with a pair of for-
ceps, move the appendage, and notice that, as it moves,
the flabellum moves up and down over the outer surfaces
of the gills.

3. Pass a bristle into the opening above the base of the
second maxilla, and notice that it passes into the branchial
chamber outside the bases of the gills.

4. Underneath the external mandibular muscle notice a
smooth, transparent elevated, chitinous ridge, the exhalent
channel, through which the water passes away from the
branchial chamber. Notice that the bristle passes through
this channel.

5. Turn the tips of the gills back, in order to expose
their inner surfaces, and notice that the lamellte are united
to each other by an internal hollow stem, the vessel which
carries the aerated blood down to the bases of the gills,
and then up to the pericardium.

6. Notice that there is an internal branchial chamber
between the gills and the flancs. Pass a bristle into the
opening at the base of the third maxilliped, and notice
that its inner end projects into the internal branchial
chamber.

7. At the bottom of this chamber notice a flabellum like
that in the outer chamber. Move the third maxilliped,
and notice that the inner flabellum moves at the same time.

GENERAL ANATOMY OF A CRAB.

197

In the anterior portion of the inner chamber notice a much
smaller flabellum which is carried by the second max-
illiped.

8. Disarticulate and remove the three maxillipeds with
their flabella, in succession, and notice again the form
and position of the flabellum of each of them.

9. Notice that while each gill is free from those on each
side of it, and from the outer and inner walls of the
branchial chamber, it is enclosed by a tough chitinous

FIG. 101.

FIG. 101. — Upper surface of the "cardiac" pouch of the stomach of
Callinectes hastatus ; with the muscles removed to show the gastric mill.
(Drawn from nature by W. K. Brooks. )

(For explanation of letters, see Fig. 102.)

cuticle, which is continuous, at the base of the gill, with
the calcified shell. "\Vhen the shell is moulted the chitin-
ous covering of the gills is also pulled off, as part of the
cast shell.

10. Place a living specimen in water, and notice the
current which is drawn through the slit at the base of

198 HANDBOOK OF INVERTEBRATE ZOOLOGY.

the third maxilliped, into the inner branchial chamber and
out from the outer branchial chamber to the opening above
the second maxilla where the water is bailed out by the
scaphognathite, and swept away from the body in a current
which flows forwards, between, and under the maxillipeds.
11. Carefully cut away the carapace of a living speci-
men in order to expose the gills and heart. Notice the
play of the flabella in the branchial chamber, and the

771

FIG. 102.

FIG. 102. — Inside view of posterior portion of "cardiac" pouch of
the stomach of Callinectes hastatus. (Drawn from nature by W. K.
Brooks. )

Explanation of the reference letters in Figs. 101 and 102 : —
a. Pterocarcliac ossicle. 6. Zygocardiac ossicle, c. Pyloric ossicle.
d. Urocardiac ossicle, e. Prepyloric ossicle. /. Opening into pyloric
pouch, g. Valvular fold over the opening of the oesophagus, h. Zygo-
cardiac tooth. i. Bottom of stomach, j. Inferior accessory ossicles.
k. Accessory cardiac tooth. I. Superior accessory ossicles, m. Opening
of oasophagus. n. (Esophagus, p. Posterior end of stomach, c p. Car-
diac pouch.

rhythmical beating of the heart. Make a small opening
through the pericardium, and introducing a few drops of
some colored fluid, such as finely-powdered carmine in
water, notice the manner in which it is drawn through the

GENERAL ANATOMY OF A CRAB.

199

ostia into the heart, to be forced out again through the
arteries at each contraction.

u. The Digestive Organs.

These are the mouth appendages, the oesophagus, the
stomach, thepyloric coeca, the liver, the intestine, and the
intestinal coecum.

Fro. 103.

Pio. 103. — Female specimen of Callinectes hastatus ; opened from below
to show the reproductive organs. (Drawn from nature, by J. E. Arm-
strong. )

A. Antennules. An. Antennae. E. Eyes, a 6. Abdomt i. b. Pyloric
pouch of stomach, c. Cardiac pouch of stomach. ./. Intesth •. TO. Man-
dible. 6. Crossbar of ovary, o P. Ovary. 7). Seminal recepk ^le. q. In-
testinal coecum. p I. Abdominal appendages, r. Oviduct.

;

200

HANDBOOK OF INVERTEBRATE ZOOLOGY.

1. The stomach consists of two portions or chambers:
the large transparent membraneous "cardiac" pouch (Figs.
103 and 104, e) which tills the anterior median portion of
the bod}", and which, as already noticed, is exposed when
the carapace is removed, and a posterior, much smaller
"pyloric" pouch (Figs. 10.") and 104, //). Raise up the
posterior border of the " cardiac " pouch and under it, at a

FIG. 104.

FlG. 104. - jlalo specimen of Callim-ctos hastatus; opened from below
to show the reproductive organs. (Drawn from nature by J. E. Arm-
strong. )

t. Testi . t- d. Vas deferens. e d. Ejaculatory duct. Other letters
as in Fijr 103.

GENERAL ANATOMY OF A CRAB. 201

somewhat lower level, notice the small pyloric pouch, with
firm, thick, greatly folded walls.

2. Turn the "cardiac" pouch to one side, and notice
the short, wide oesophagus which runs up from the mandi-
bles to open on its lower floor. Notice that a great part
of the "cardiac" pouch is anterior to the oesophagus.
Pass a bristle between the mandibles, through the mouth
and oesophagus, and notice that it projects into the cardiac
pouch.

3. The liver is a very large organ, which not only runs
out along the edge of the carapace, as shown at i in Fig.
100, but also runs under the stomach and the heart, and
fills the greater part of the body cavity. Notice that it is
divided up into lobules, and carefully examining one of
these lobules, notice that it consists of great numbers
of small hepatic tubules, which are so loosely bound to-
gether that they readily separate from each other, or "fray
out." Notice that the tubules converge on each side of
the body to form an hepatic duct, which opens into the
pyloric chamber of the stomach.

4. The "pyloric" coeca. These are a pair of long,
slender, white, convoluted tubes, which are twined be-
tween the ovaries, the liver, and the mandibular muscles,
on each side of the pyloric pouch, into which they open.

5. The intestine (Figs. 103 and 104 i) is a long, straight,
transparent, dark-colored tube, which runs along the mid-
dle line of the bod}' below the heart and posterior branches
of the ovary, from the pyloric pouch to the anus, which is
on the ventral or upper surface of the tip of the abdomen.

6. The intestinal coecum is a long coiled tube (Figs.
100, 103, and 104, q) which opens into the intestine in
the second abdominal somite. It consists of two parts : a
convoluted portion which forms a compact ball (Fig.

202 HANDBOOK OF INVERTEBRATE ZOOLOGY.

100, q) back of the heart, and usually on the right, some-
times on the left side of the intestine, and a straighter por-
tion which runs back from the coiled portion to open into
the intestine.

7. The gastric mill. Notice once more the anterior and
posterior gastric muscles which inn from the cardiac pouch
to the carapace ; clean them off, and notice, in the wall of
the cardiac pouch a pair of stiff, white, calcareous rods
(Fig. 101, a), the pterocardiac ossicles, which meet each
other on the median line, while their slender, outer ends
run outwards and downwards onto the sides of the
stomach, where they join the cardiac later o-super lor ossicles
or zygocardiacs (Fig. 101, b). These incline backwards,
upwards, and inwards, and their hinder ends join a small
transverse bar, the pyloric ossicle (Fig. 101, c) which lies
near the posterior end of the stomach. The pterocardiac
and pyloric ossicles are joined to each other by a pair of
median gastric muscles (Fig. 100, c) ; and, removing these,
note that they do not lie on the surface of the stomach,
but that they roof over a deep, conical depression pro-
duced by an infolding of the stomach-wall between the
pterocardiac and pyloric ossicles. From the point of
union of the two pterocardiac ossicles, a stout bar, the
urocardiac ossicle (Fig. 101, d) runs downwards along
the anterior edge of this pit, while a much smaller pre-
pyloric ossicle (Fig. 101, e) runs from the middle of the
pyloric ossicle (c) along the posterior face of the pit, to
join the lower end of the urocardiac ossicle.

Turn the stomach to one side, and, cutting the oesopha-
gus and intestine, remove it from the body, and notice in
a side view the large, thin-walled cardiac pouch and the
much smaller, thick-walled pyloric pouch. Carefully clear
away the layer of muscles which forms the greater part of

GENERAL ANATOMY OF A CRAB. 203

the stomach- wall, and notice that it is lined by a tough,
thin, transparent, chitinous coat, which is thickened and
calcified at certain points to form the ossicles of the gastric
mill. Open the cardiac pouch in front, to expose the
opening into the pyloric pouch and the ossicles which sur-
round it, and spreading it out notice again : —

(i.) The pterocardiac ossicles (Fig. 102, a).

(ii.) The urocardiac ossicle (Fig. 102, cT), projecting
downwards and backwards, in front of the opening (f)
into the pyloric pouch, and ending below in a dense uro-
cardiac tooth.

(iii.) On each side of and a little anterior to this tooth,
notice the zygocardiac teeth (Fig. 102, A), two dense,
thick, dark-colored prominences, which are carried upon
the inner sides of the zygocardiac ossicles (6), and which
have their inner surfaces marked by ridges and furrows,
something like the molar teeth cf a rodent.

(5v.) On the floor of the stomach notice the opening (g)
of the oesophagus, guarded by valvular folds of the wall
of the stomach, and posterior to the mouth, a groove or
channel (i) which runs backwards to the pyloric orifice (/),
where it ends in an inferior cardiac tooth, which lies a
little behind and below the tip of the urocardiac tooth.

(v.) On each side of this gutter notice a large, triangular
plate (j), the inferior accessory cardiac ossicle, the inner
edge of which forms the wall of the gutter, and is marked
by a number of parallel ridges.

(vi.) Above this on each side a long slender superior
accessory cardiac ossicle (?), which runs downwards and
imvards from the anterior end of the zygocardiac ossicle,
to terminate in a soft, hand-like tooth (A1), with a number
of slender, finger-like processes. This is the accessory
cardiac tooth.

204 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(vii.) Study in another specimen the way in which these
ossicles are moved upon each other by the gastric muscles,
and make drawings of the outer and inner surfaces of the
stomach.

v. The antennary glands. After removing the stomach,
notice on each side of and a little anterior to the oesopha-
gus, and in front of the mandible, the flat, coiled, greenish-
white antennary gland.

iv. The female reproductive organs. These vary in size
according to the season. They consist of the ovary, two
seminal receptacles, and the oviducts.

1. The ovary consists of two lateral portions (Fig.
103, ov, ov), which run from the outer angles of the
carapace along its anterior border, and then backwards,
inwards, and downwards, along the stomach, and then
upwards and backwards on each side and a little above the
intestine as far as and sometimes into the first abdominal
somite, and a median portion or cross-bar (Fig. 103, o)
which joins the two lateral halves just above the pyloric
pouch of the stomach.

2. The seminal receptacles, (Fig. 103, p) are two
pouches which vary greatly in size according to the season.
They are on the inner surface of the sternal plastron, and
each communicates, on its upper surface, with one of the
lateral divisions of the ovary.

3. The oviducts are very short tubes, which run from
these pouches to the female reproductive orifices, in the
sternum of the somite which carries the third pair of
pereiopods.

4. Dissect out and draw the female reproductive
organs.

5. If a female is found carrying eggs, notice the man-
ner in which they are fastened to the hairs of the abdominal
appendages and covered by the abdomen.

GENERAL ANATOMY OF A CRAB. 205

x. The reproductive organs of the male crab.

The testis (Fig. 104, t) is very similar to the ovary, and
consists of two lateral portions and a cross-bar. Each
lateral portion gives rise to a very long, greatly convoluted,
transparent white tube, the vas deferens (Fig. 104, vd),
which passes into a straighter portion, the ejaculatory
duct (ed), opening on the coxopodite of the fifth pereiopod.
Carefully examine the base of this joint, and notice that
the duct is prolonged, outside it, as a soft white tube,
which runs into the base of the first pleopod, into which it
opens.

y. The Nervous System.

Another specimen should, if possible, be used for study-
ing the nervous system. It should be opened from above
by cutting away the carapace, and, if a fresh specimen is
used, it should be placed in seventy-five per cent alcohol
as soon as it is opened, and the dissection should be carried
on under the alcohol.

Turn the cardiac pouch to one side, and notice on the
lower surface of the anterior portion two white small gas-
fric ganglia, each of which is joined to a large nerve,
which runs forwards to the floor of the anterior edge of
the carapace, near which it enters the outer end of one of
the cerebral ganglia. These are a pair of pear-shaped
ganglia, united to each other on the middle line of the
body, and giving off from their narrow ends nerves to the
eyes, the antennas, the antennules, the gastric ganglia, and
the lining of the carapace.

They also give rise to a pair of msophageal commissures,
or small nerves which run backwards, one on each side of
the oesophagus, into the cavity of the sternal plastron.
Just behind the oesophagus these commissures are united
to each other by a transverse commissure ; and at the outer

206 HANDBOOK OF INVERTEBRATE ZOOLOGY.

ends of this, on the longitudinal commissures, are a pair
of small ganglionic enlargements, which give rise to a pair
of small nerves to the muscles of the mandibles, and also
to a small pair which run up onto the stomach, to the gas-
tric ganglia.

Trace the longitudinal commissures backwards into the
sternal plastron, where they join the thoracic ganglia, a
white ring, perforated in the centre, and giving off, on
each side, nerves to the maxillse, the maxillipeds, and the
pereiopods. The sternal artery passes through the ring.
Carefully examine the ring with a lens, and notice that it
is made up of a number of small ganglia fused together,
but still showing traces of their separate outlines. Notice
a small nerve which runs backwards from the ring into the
abdomen.

z. The Auditory Organs.

Cut away the external or lower surface of the large
basal joint of the antennule, and notice that it is almost
entirely filled by the auditory sac, an irregular, greatly
folded vesicle, the wall of which is chitinous, but somewhat
flexible. Notice that the wall of the sac is united to the
inner surface of the upper side of the shell which covers
the basal joint of the antennule. The sac has no external
opening, but a line, fringed with hairs, on the outer sur-
face of the joint, marks the line along which it is joined
to the shell. Cut the sac out, and opening, notice that it
does not contain any grains of sand or other solid bodies.
Examine its inner surface, under water, with a hand-lens,
or a low power of the microscope. Notice a row of long,
slender auditory hairs, which project from the wall into
the cavity of the sac. There are also great numbers of
much smaller hairs scattered irregularly over the inner
surface of the sac.

THE METAMORPHOSIS OF A CRAB. 207

XXI. THE METAMORPHOSIS OF A CRAB.

(Callinectes hastatus.)

THE material gathered at the surface of the ocean with
the dip-net, as described in Section VII. , will usually be
found to contain specimens of the various stages in the
metamorphosis of crab-larvae. They are all sufficiently
alike to be used in verifying the following description ; so
it is not necessary to obtain the larvae of Callinectes.

I. The Zoea /Stage. If the water which has been col-
lected with a dip-net on a calm summer evening be placed
in a glass beaker and held before a light, numbers of crab-
zoeas will usually be found. They are very active, and
they show a slight tendency to collect at the surface on the
side nearest the light, although they may be found swim-
ming in all parts of the beaker. They may be recognized
by comparison with Fig. 105, which is a highly magnified
side view of the zoea of Callinectes about twelve hours
after its escape from the egg.

Catch several zoeas with a dipping-tube, and placing
them in a watch-crystal with a small quantity of sea- water,
examine them with a power of from fifty to one hundred
diameters, and notice : —

a. The very large compound eyes (Figs. 105 and
106, E).

b. The shell, or carapace (Figs. 105 and 106, c), which
covers up the anterior portion of the body.

c. The long, movable, jointed abdomen («) which pro-
jects from underneath the posterior edge of the carapace,
and ends in a large, forked telson.

d. Between the eyes the carapace is prolonged down-
wards to form a long, slender, pointed rostrum (Figs. 105

20«

HANDBOOK OF INVERTEBRATE ZOOLOGY.

and 106, r), the length of which varies greatly in different
species.

e. Near the posterior edge of the middle of the dorsal
surface the carapace is prolonged to form a slender, pointed
dorsal spine (Figs. 105 and 106, d), the length of which
also varies greatly in different species.

FIG. 105.

FIG. 105. — Zoea of Callinectes, one day after hatching, seen from the
left side, magnified about eighty diameters. (Drawn by W. K. Brooks
from a sketch from nature by E. B. Wilson. )

A. Antennule. An. Antenna, a. Abdomen, c. Carapace, d. Dor-
sal spine. E. Eye. L. Labrum. I. Lateral spine, mp1. First maxilli-
ped. mp2. Second maxilliped. r. Rostrum, t. Telson.

f. In Callinectes the sides of the carapace give rise to a
pair of shorter lateral spines (Figs. 105 and 106, 6), which
are absent in the zoeas of many crabs.

THE METAMORPHOSIS OF A CRAB.

209

g. Notice the transparent, pulsating heart, at the base
of the dorsal spine, and the intestine, running from under-
neath the carapace out to the tip of the abdomen, to open
at the anus, between the forks of the telson. Notice that
the intestine dilates a little near the anus, to form an en-

FlG. 106.

FIG. 106. — Anterior view of the same zoea. (Drawn by W. K.
Brooks from a sketch by E. B. Wilson. )

The reference letters are the same as those of Fig. 105.

larged rectum, which is attached to the integument by a
number of small, radiating muscular fibres, and is rhyth-
mically contractile like the heart. The enlarged stomach
and liver may be obscurely seen through the side of the
carapace.

210

HANDBOOK OF INVERTEBRATE ZOOLOGY.

h. Notice the two pairs of swimming feet (Figs. 105
and 106, mpl, rap2), which project beyond the lower edge
of the carapace, and end in long swimming hairs. They
are the first and second pairs of maxillipeds, which are
organs of locomotion in the zoea, but mouth-parts in the
adult crab.

i. Notice the antennules (Fig.
105, A), and the antennae (An) pro-
jecting downwards behind the ros-
trum. They vary greatly in size in
different zoeas, and may be much
longer or much shorter than they are
in Callinectes.

j. A large rounded labmm (Fig.
105, L) lies on the middle line of
the ventral surface, and between it
and the bases of the maxillipeds are
the mandibles, and two pairs of
maxillce.

FIG. 107. — Antennule and antenna of the
zoea shown in Fig. 105. (Drawn by W. K.
Brooks from a sketch by E. B. Wilson.)

A. Antennule. An. Antenna.

k. Make a sketch of the zoea showing these points.

I. Place a zoea on a glass slide in a drop of sea-water,
and laying a piece of paper near it to support the cover-
glass, gently cover it, and examine it with a higher power,
noticing : —

. 1. The antennules (Fig. 107, A). Each consists of a
short swollen basal joint, which carries two long sensory
hairs, and, in Callinectes, a third much shorter hair.
Notice that the two long hairs do not taper, but are uni-
formly thick from base to tip.

FIG. 107.

THE METAMORPHOSIS OF A CRAB. 211

2. The antennae (Fig. 107, An). These consist of two
portions : a spine, which in Callinectes is about as long as
the rostrum, and is fringed with short hairs ; and a shorter
movable exopodite, or scale, which springs from near the
base of the spine, and ends in two slender, tapering hairs.
The scale corresponds to the scale at the base of the an-
tenna of a lobster or crayfish, and the flagellum of the
antenna of the adult crab is absent in the newly hatched
zoea.

3. The labrum (Fig. 108, L). This is a rounded, pro-
jecting, hood-like organ, which is usually marked by a
conspicuous dendritic pigment spot. Its posterior free
edge is fringed with short hairs.

4. The mandibles (Fig. 108, M ). These are usually
marked by pigment spots, and their cutting edges have
two or three hook-like points or " teeth." The mandibles
are not exactly alike, the left differing from the right a
little. The palpus carried by the mandible of the adult
is entirely absent in the zoea.

5. The first maxilla (Fig. 108, Mx1) consists of three
portions : a basipodite (b), a coxopodite (ex), and an endo-
podite (en).

The basipodite and coxopodite together make up the
long protopodite or body of the maxilla, and their inner
edges are fringed with stout plumose hairs. The endopo-
dite is more slender, two-jointed, and it ends with a few
long slender plumose hairs.

6. The second maxilla (Fig. 108, Mx2) consists of a
protopodite (p), an endopodite (en), and an exopodite or
scaphognathite (.sc). The protopodite is made up of a
small coxopodite (ex) and a much larger basipodite (6).
The free inner ends of these joints are notched or bilobed,
and carry long, slender, plumose hairs. The tip of the

212

HANDBOOK OF INVERTEBRATE ZOOLOGY.

single-jointed endopodite is also bilobed, and carries four
long plumose hairs. The scaphognathite is a flattened
plate, with a long plumose hair at its distal end, a much
stouter one at its proximal end, and three smaller ones

MX J

MX 2

FIG. 108.

PIG. 108. — Mouth-parts of the zoea shown in Fig. 105, seen from
below. (Drawn by W. K. Brooks from sketches by E. B. Wilson.)

L. Labrum. M. Mandible. Mxl. First maxilla. Jtfx2. Second max-
illa. 6. Basipodite. ex. Coxopodite. en. Endopodite. p. Protopodite.
sc. Exopodite or scaphognathite.

THE METAMORPHOSIS OF A CRAB.

213

along its outer edge. These hairs are much more finely
plumose than those on the other mouth-parts.

7. The first maxilliped (Fig. 109, Mpl). This con-
sists of a large muscular protopodite, which carries an
exopodite (ex) and an endopodite (en) . The exopodite is

FIG. 109.

FIG. 109. — Maxillipeds of the same zoea. (Drawn by W. K. Brooks
from a sketch by E. B. Wilson. )

Mp1. First Maxilliped. Mp'2. Second maxilliped. ex. Exopodite.
en. Endopodite.

two-jointed, flattened, and is usually bent upwards against
the side of the carapace. It ends in four long, two-jointed,
plumose swimming-hairs. The endopodite is about as

214 HANDBOOK OF INVERTEBRATE ZOOLOGY.

long as the exopodite, cylindrical, and five-jointed. It
ends with two long plumose hairs and two shorter simple
hairs.

8. The second maxiUiped (Fig. 109, Mp2). This is
much like the first maxilliped, but its endopodite is rudi-
mentary.

These are all the appendages which are present in the
newly-hatched zoea of Callinectes, but in the older zoea
of this species, and in the newly-hatched zoeas of many
other species a nearly Vertical series of bud-like protuber-
ances will be seen underneath the edge of the carapace,
between the base of the second maxilliped and the first
segment of the abdomen. These buds are the rudimen-
tary third maxillipeds and the pereiopods.

9. Make careful drawings of the appendages of the zoea,
and compare them with the corresponding appendages of
the adult.

10. The abdomen (Figs. 105 and 106, «). This consists
of five free segments, the sixth being fused with the telson.
The telson is deeply forked, the anus is in the notch of the
fork, and on each side of it there are a number of plumose
hairs : three hairs in the newly-hatched zoea of Callinectes,
but none in some other species. The pointed prong of the
telson carries two movable hairs or spines, which are not
plumose.

11. Make a sketch of the telson.

m. The HJmbryonic Zoea. A few minutes after hatch-
ing, the zoea of Callinectes has the form above described ;
but if a crab zoea be taken immediately after leaving the
egg, it will be found to be enclosed in a delicate, trans-
parent, embryonic skin, which is very quickly stripped off
as soon as the larva begins to swim. Place a female crab
with eggs in an aquarium, and, keeping her until the eggs

THE METAMORPHOSIS OF A CRAB. ' 215

hatch, place some of the larvse under the microscope, and
examining them very carefully with a high power, notice
the larval skin, which conforms very closely to the outline
of the body of the zoea except upon the antennules, the
antennae, and the telson. The embryonic antennule is
very much larger and longer than that of the zoea, and it
carries a long, hairy branch, and a second much shorter
branch. The antenna of the embryonic skin is also very
much larger than that of the zoea. It divides near its
base into two branches, one of which is short and blunt,
while the other ends in three long, plumose, swimming-
hairs. The telson of the embryonic skin is also very much
larger than that of the zoea, and is a slightly-forked fan-
like organ, with seven pairs of large, transparent, swim-
ming-hairs, five of them plumose.

n. The Older Zoea.

The zoea sheds its skin a number of times, the bud-like
rudiments of the third maxillipeds and pereiopods grow a
little, and the portion of the body which carries them be-
comes obscurely divided into segments, the abdominal feet
or pleopods make their appearance as pairs of buds on the
ventral surface of the abdominal segments, and the endo-
podite or flagellum appears upon the antenna, and the palp
on the mandible.

For a number of moults the change of the larva is
gradual ; but after a time it sheds its skin and becomes
suddenly converted into a larva which is quite different
from the zoea, and which is known as a Meyalops.

II. The Mecjalops Stage (Fig. 110). The megalops
larvae may easily be reared from zoeas, or they may be
obtained by surface-collecting. They are able to swim
actively, but they frequently cling to the sides of the glass
beaker, where they may be recognized by their resem-

216 HANDBOOK OF INVERTEBRATE ZOOLOGY.

blance to small crabs. Catch two or three specimens with
a dipping-tube, and place them in a tumbler of sea-water,
where they may be kept alive for examination.

a. Place one of them in a watch-crystal, in enough sea-
water to cover it, and, examining it with a low power,

FIG. no.

FIG. 110. — Megalops of Callinectes or of a closely-allied crab, magni-
fied about eighty diameters. (Drawn from nature by W. K. Brooks.)

A. Antennule. An. Antenna, ab. Abdomen, c. Carapace. E. Eye.
pr. 5, Fifth pereiopod. r. Rostrum. L Fifth thoracic somite.

notice that it differs from the zoea and resembles the full-
grown crab in the following respects : —

THE METAMORPHOSIS OF A CRAB. 217

1. The carapace (Fig. 110, c) has no lateral spines, and
either no dorsal spine or a very small one.

2. The eyes (Fig. 110, E) are at the ends of very
movable stalks.

3. The five pairs of pereiopods are fully developed, and
are very similar to those of the adult.

4. The gills have made their appearance, above the
bases of the pereiopods, under the lateral margin of the
carapace, but these margins are still free, as they are in
the zoea.

5. The maxillipeds are no longer organs of locomotion,
and there are three pairs.

6. While the larva is still able to swim, it also moves
over the bottom by walking upon the tip of the pereiopods,
with a crab-like gait, very similar to that of the adult.

b. It differs from the adult in the following conspicuous
features : —

1. There is a long, pointed rostrum (Fig. 110, r) at
the anterior end of the carapace.

2. The eyes (E} are not covered by the carapace, and
they are not upon the anterior edge, but upon the sides of
a median frontal region.

3. Both antennules and antennae project from beneath
the edge of the carapace, and the flagella of the an-
tenna (-4») are very long.

4. In Callinectes, and in many other species, the fifth
pair of pereiopods (pr. 5) are bent upwards and backwards
above the dorsal surface of the carapace.

5. The segment (7) which carries them is movable.

6. There is a long, movable, six-jointed abdomen (a&),
which carries five or six pairs of biramous swimming-feet,
and ends in a small, rounded telson. While the animal is
swimming the telson is stretched out behind the carapace,

218 HANDBOOK OF INVERTEBRATE ZOOLOGY.

but while crawling it may be bent forwards under the ven-
tral surface of the fore-body, as in the adult.

c. Make a drawing of the megalops larva, showing as
many of these points as possible.

d. Examine the appendages more carefully, dissecting
them out with needles, and notice : —

1. The basal joint of the antennule (Fig. 110, A) is
swollen, and the otocyst ifiay be seen through the trans-
parent integument. Its opening on the upper surface is
fringed by a few long hairs, which project beyond the edge
of the carapace.

2. The flagellum of the antenna (Fig. 110, An) is com-
paratively very much longer than it is in the adult, and
single. The basal joints of the antenna are not very much
larger or longer than the terminal joints, and it is not
doubled back under the carapace.

FIG. 111. —First maxilla of the Megalops
of Portunus. (From Claus, Untersuchen
zur Erforschuny der Genealogischen
Grundlage des Crustaceen- Systems. Taf.
xiii.)

1. Coxopodite. 2. Basipodite. en. En-
FIG. ill. dopodite.

3. The mandible is very similar to that of the adult,
and carries a jointed palp.

4. The first maxilla (Fig. Ill) is very similar to that
of the adult, but the hairs upon its basal joints are less
numerous, and comparatively very much longer.

5. Tho second maxillae (Fig. 112) also have larger and
less numerous hairs, and the seaphognathite (sc) is fringed
with hairs around its entire edge.

6. The exopodite (ex) of the first maziUiped (Fig. 113)
is quite like that of the zoea, and carries four long hairs,

THE METAMORPHOSIS OF A CRAB.

219

and lacks the many-jointed tip which is found in the adult.
The endopodite (en) is free from the exopodite, and has
only a few hairs, but in other respects it is similar to that
of the adult, and very different from that of the zoea.
The appendage carries a long flabellum (/), which pro-
jects into the gill-chamber, and is like that of the adult,
but with only a few long
hairs. The basal joints
of the appendage (1 and
2} are very different from
those of the zoea, and are
very similar to those of

the adult.

FIG. 112. — Second maxilla

of the same larva. (From
Claus. )

1. Coxopodite. 2. Basipo-

dite. en. Endopodite. sc. Scar
phognathite.

FIG. 112.

7. The exopodite of the second maxilliped (Fig. 114, ex)
is like that of the zoea, but in other respects the append-
age is like that of the adult.

8. The third maxilliped (Fig. 115) is fully developed,
and much like that of the adult, except that the basal
joints of the endopodite are not flattened to form a mouth-
cover, or gnathostegite, and the gill is carried upon the
basal joint of the limb, instead of upon the episternum.

9. The pereiopods (Fig. 116) are essentially like those
of the adult, except that their gills are upon their basal
joints.

10. The abdominal appendages. These are carried by
all or by the last five abdominal somites, and each consists

220

HANDBOOK OF INVERTEBRATE ZOOLOGY.

of a basal portion and two hairy paddles ; but the endopo-
dites of opposite sides join each other on the middle line.

e. Observe that the abdomen
and abdominal appendages of the
megalops larva are much more like
en --VA/ V those of the adult female than those
of the adult male.

FIG. 113.

FIG. 113. — First maxilla of the same larva. (FromClaus.)
1. Coxopodite. 2. Basipodite. en. Endopodite. ex. Exopodite.
/. Flabellum.

FIG. 113. — Second maxilliped of the same larva. (From Claus.)

a. Coxopodite. b. Basipodite. c. Ischiopodite. d. Meropodite.

e. Carpopodite. /. Propodite. g. Dactylopodite. en. Endopodite.

ex. Exopodite. gi. Gill.

/. Make drawings of the appendages of the megalops
larva.

g. Carefully compare the various parts of the megalops
larva with those of the adult crab, and with those of a
lobster or crayfish, and notice that the larva resembles the
lobster in the following points of difference from the
adult : —

1. There is a rostrum.

THE METAMORPHOSIS OF A CRAB.

221

2. The lateral margins of the carapace are free from the
body.

3. The antennae are long.

4. The third maxillipeds are not flattened.

5. The gills are on the basal joints of the limbs.

6. There is a free, movable, jointed abdomen, used in
locomotion.

7. There are numerous biramous swimming abdominal
appendages.

8. There is a free telson.

FIG. 115.

FIG. 116.

FIG. 115. — Third maxilliped of the same larva. (After Claus.)
Letters as in Fig. 114.

FIG. 116. — Pereiopod of the same larva. (After Claus.)
Letters as in Fig. 114.

h. Keep a larva in confinement until it changes into the
young crab (Fig. 117).

i. The auditory organ. The integument of the megalops
larva or of the very young crab is sufficiently transparent
to render the examination of the hearing organ possible

222

HANDBOOK OF INVERTEBRATE ZOOLOGY.

without dissection, .and the young stages are therefore more
favorable than the adult crab for studying the organ.

FIG. 117. — Young crab which moulted from the Megalops shown in
Fig. 110. (Drawn from nature by W. K. Brooks.)

Place a megalops larva in a watch-crystal, in a few drops
of water, and covering it with a thin glass cover, to keep

ANATOMY AND METAMORPHOSIS OF CYCLOPS. 223

it quiet, examine the basal joints of the antennules with
the highest magnifying power that can be used (from fifty
to one hundred diameters). Notice the thin-walled, trans-
parent vesicle, the otocyst, which nearly fills the enlarged
basal joint of the antennule. On the upper surface of the
antennule notice the transverse slit through which the oto-
cyst opens to the exterior. Notice the row of hooked
hairs which project over this slit, as a sort of thatch. In
the cavity of the otocyst a number of small grains of sand.
A row of long, slender, sensory hairs, which project from
the wall of the otocyst into its cavity, on the side nearest
the median line of the body. On the posterior or basal
side an irregular cluster of shorter hairs.

An examination of the hearing organ of the adult crab,
and of the lobster or crayfish, will show that the megalops
larva differs from the adult and resembles the lobster, in
having the otocyst open to the exterior. The grains of
sand also are present in the otocysts of the lobster, but
absent in that of the adult crab.

XXII.— THE ANATOMY AND METAMORPHOSIS OF
CYCLOPS.

SMALL Copepods are usually abundant in both fresh and
salt water, and there is never any difficulty in obtaining
them. As Cyclops is one of the most common and widely
diffused fresh- water genera it has been selected for de-
scription, but there should be no difficulty in studying other
forms, for although the generic differences are very con-
siderable, they are not of such a character as to confuse
the student. In order to obtain a supply of specimens of
Cyclops, carefully examine the sides of an aquarium in
which water plants have been growing, and search for

224

HANDBOOK OF INVERTEBRATE ZOOLOGY.

very minute, active white animals, about a twenty-fifth of
an inch in length. When one of these white specks comes
to rest upon the side of the glass, pass a dipping-! ul>o
down to it, and removing the finger from the top, allow
it to be drawn into the tube. Transfer it to a watch-
glass, and, examining it with a
low magnifying power, ascertain
whether it resembles Fig. 118,
either with or without the egg
bunches (n) ; if so, it is a
Copepod. The females of the
fresh-water species are larger
and very much more abundant
than the males, and as they
are therefore the most easily
obtained, this account has been
written with especial reference
to the female, except when the
contrary is stated.

FIG. 118. — Dorsal view of female
specimen of Cyclops canthocarpoides,
with ovisacs highly magnified. (From
Claus, Freilebenden Copepoden.)

a. First antennae, b. Ocellus, c. Ovi-
duct, d. Carapace. e, /, g, h. The
four free thoracic somites. i,j,k,l. The
FIG. 118. abdominal somites, n. Ovisacs.

A number of females should be placed in a watch-crystal
with only enough water to cover them, and killed by add-
ing a small quantity of ether to the water. One or more
individuals will then probably be found to present a good
view of the dorsal surface for microscopic examination.

I. In the dorsal view notice that the body is divided
into two regions of nearly equal length ; an anterior

ANATOMY AND METAMORPHOSIS OF CYCLOPS. 225

larger, pear-shaped, segmented ceplialoihorax, and a nar-
row segmented abdomen, which is forked posteriorly and
ends in two bunches of long hairs, which make up a little
more than half the total length of the abdomen.

a. The cephalotliorax. This is made up of an anterior
unsegmented carapace, which is followed by a number of
free thoracic somites.

1. The carapace (Fig. 118, d) is broad and a little
longer than wide, and forms about a third of the entire
length of the animal. Its anterior margin is rounded at
the sides, but the even curve is a little* broken on the
anterior median line, which is occupied by a short rounded
rostrum.

(i.) Upon the base of the rostrum, in the median line
of the body, note the single dark brown eye-spot (b). A
higher power shows that this is formed by the fusion of a
pair of eyes, and the two lenses may be seen upon the
sides of the spot.

(ii.) Projecting from below the sides of the rostrum
are the. large, many-jointed first antennas (a), which bend
backwards along the margins of the carapace, and carry a
number of scattered hairs upon their anterior edges.

(iii.) Beside and below these are the shorter jointed
second antennae.

2. Posterior to the carapace the dorsal surface of the
cephalotliorax is formed by the movable terge of the four
free thoracic somites (e, f, g, h) . These are of about equal
length, but they gradually decrease in width from before
backward ; the first being nearly as wide as the carapace,
and the fourth only about half as wide.

b. Back of the last thoracic somite is the narrow,
slightly tapering abdomen, divided into four apparent
segments.

226 HANDBOOK OF INVERTEBRATE ZOOLOGY.

1. The first of these (z) is longer than it is wide, and
its manner of development, as well as a comparison of the
female abdomen with that of the male, shows that it is
formed by the union of two somites.

The ovisacs (n) are attached to the sides of this
segment, and the apertures of the oviducts indicate the
line along which the two originally separate somites have
become united.

2. The three following abdominal somites (/, &, ?) are
narrow, and the anal orifice may be seen near the centre of
the dorsal surface of the last, which carries a pair of diver-
gent segmented styles (w), each of which carries four
plumose setae.

c. Notice the free setose ends of the thoracic append-
ages projecting beyond the edges of the free thoracic
somites.

d. Make a sketch of the dorsal surface, showing all
these points.

II. In order to get a satisfactory side or ventral view the
animal may be placed upon a glass slide with a small drop
of water, and then moved into the desired position with a
needle. A small piece of paper should be placed near
the specimen to support the cover-glass, which will be
necessary for the satisfactory study of this aspect. In a
side or ventral view note : —

a. The shell-glands; a pair of convoluted, transparent
tubes, one on each side near the middle of the ventral
margin of the carapace.

b. The mouth is upon the median ventral line near the
anterior end, and is bounded anteriorly by a projecting
labrum. Its posterior margin is formed by a bilobed
ridge, the metastoma, which can be satisfactorily made out
only in a ventral view.

ANATOMY AND METAMORPHOSIS OF CYCLOPS. 227

c. The appendages.

1. The large jointed first antennse have been already
noticed. They are the principal locomotor organs, and
are seen, in a side view, to be the first or most anterior
pair of jointed appendages.

2. Next posterior to these are the second antennse,
which have already been noticed.

3. On the sides of the mouth are the
stout, blunt, dark-colored mandibles
(Fig. 119).

FIG. 119. — Mandible of Cyclops canthocar-
poides. (From Claus.)

FIG. 119.

FIG. 120.

4. Behind these are the incurved setose
first maxillce (Fig. 120), which, like the
mandibles, have cutting edges.

FIG. 120. — First maxilla of Cyclops canthocarpoides.
(From Claus.)

5. The second maxillce (Fig. 121) are jointed, and con-
sist of two portions, the exopodite (ex.), which is much
the larger, and, in a side VICAV, is anterior to the smaller-
jointed endopodite (en). These parts are mounted upon
a protopodite, which, as well as the exopodite and endopo-
dite, carries plumose setae. The proximal portion of the
exopodite carries three distal joints, which are placed side
by side, and may be folded down upon the proximal por-
tion, like fingers bent down into the palm of the hand.

6. Considerable space intervenes between the mouth-
parts and the thoracic appendages, of which there are five
pairs, the four anterior pairs being about equal in size,
and the fifth pair rudimentary. The first pair of limbs

228 HANDBOOK OF INVERTEBRATE ZOOLOGY.

lies under the posterior margin of the carapace, and the
following pairs are the appendages of the four free tho-
racic somites. Each of these appendages, the last excepted,
consists of a two-jointed protopodite, which carries an
exopodite and an endopodite, each of which is three-
jointed. All the segments of the limb carry long delicate
plumose setae upon their posterior or inner margins, and
stout, serrated, movable spines upon
their anterior or outer margins. The
fifth thoracic appendage consists of a
basal joint and two spines, which appear
to represent the exopodite and endo-
podite.

FIG. 121. — Second maxilla of Cyclops canthocar-
FIG. El. poides. ( From Claus. )

d. Near the middle of the first abdominal segment are
the large oval openings of the oviducts, one on each side
of the body. The margin of the opening is thickened and
is prolonged posteriorly into a projecting spine, which
probably serves to support the ovisacs.

e. Make a drawing of the side view, showing thc.-r
points.

III. The Digestive Tract. This is a nearty straight tube
which runs along the middle line from the mouth to the
anus. Its anterior end is large and its thick walls contain
large brown hepatic cells. The posterior portion is smaller
and more transparent, and exhibits active contractions.
In the anterior portion of the abdomen there is usually an
enlargement filled with partially-digested food, but it may
be absent, and its position is not constant.

IV. The reproductive organs of the female consist of a
single ovary, two oviducts, and a apennatkeoa.

ANATOMY AND METAMORPHOSIS OF CYCLOPS. 229

a. The ovary is in the middle line of the dorsal surface
of the carapace. Its appearance varies somewhat at
different times, and when nearly empty of eggs it is trans-
parent and almost invisible.

b. On each side of it is a long, branched oviduct (Fig.
11.8, c) which is very dark and granular at its anterior end
when distended with eggs, while the posterior portion is
more transparent and difficult to detect. The eggs are
small and transparent when they leave the ovary, but they
become larger and opaque in the oviducts.

The oviducts pass backwards to open on the sides of the
first abdominal segment, at the point a of Fig. 122, and the
opening is covered by a little lid which is fringed with
hairs, and serves for the attachment of the ovisacs.

FIG. 122. — Highly magnified diagrammatic view
of the ventral surface of the first abdominal
somite of a mature female specimen of Cyclops
brevicaudatus. (From Graber. Taf. xxvi.
Fig. 11.)

a. Setose plate of integument which covers the

external opening of the oviduct, b. Spermatic \ \ |j^/ "/ e

duct, through which the semen (e) passes from

the spermatheca (d) to the oviduct, r. Vulva, or

orifice to which the spermatophore is attached,

and through which the spermatozoa pass into the FIG. 122.

the spermatheca. d. Spermatheca. e. Spermatic fluid..

c. Under the integument of the ventral surface of the
first abdominal segment, notice a transparent oval sac,
the spermafheca (Fig. 122, d). It opens to the exterior
by a median ventral aperture, the vulva (Fig. 122, c),
through which the seminal fluid of the male passes into the
sac.

On each side of its anterior cud a small tube, the sper-
matic duct (Fig. 122, b) runs outwards and upwards to

230 HANDBOOK OF INVERTEBRATE ZOOLOGY.

open into the oviduct, close to its termination. The eggs
are fertilized while passing this opening on their way out
of the oviduct.

V. The Examination of the Male.

The males are very rarely found, but they may occa-
sionally be captured while copulating with the females.
They are. very much smaller than the females, and they
differ from them in the following respects : —

a. The first antennre are more stout than those of the
female, and near the tip of each there is a hinge-joint,
which allows the terminal portion to fold down onto the
basal portion, like a knife-blade shutting into its handle.
These antennae are the clasping organs, by which the male
clings to the abdomen of the female.

b. The male abdomen is made up of five somites, of
which the first and second correspond to the first segment
of the female abdomen.

c. The reproductive organs of the male consist of a sin-
gle median testis, and two long winding vasa deferentia.

1. The testis (Fig. 123, t) is a small compact transpa-
rent body on the median line, above the digestive tract,
under the posterior edge of the carapace. It is divided,
at its anterior end, by a notch, into two divergent
branches, each of which is continued to form, —

2. The vas deferens: a long folded tube (Fig. 123, vd)
divided into three regions.

(i.) The first division (123, vd. 1} is a delicate transpa-
rent tube, with a thick wall, and a very small central
cavity. It runs downwards and backwards to the second
or third thoracic somite, find then bends forwards again
nearly to the anterior edge of the testis. These two
bends are bound up in a single sheath. The cavity of this
portion of the vas deferens, which is simply a duct to

ANATOMY AND METAMORPHOSIS OF CYCLOPS. 231

convey the seminal fluid from the testes to the second
chamber, is usually empty, since the seminal fluid passes
through it quite rapidly to the second portions.

(ii.) The second region or spermatoph ore-forming por-
tion (vd. 2} is not abruptly separated from the first division.
It reaches from the carapace to the first abdominal somite,
and its cavity is usually distended by the spermatozoa
which have passed to it from the testes through the first
division. They are here stored up, and, as they accumu-
late, are packed together to form a complex spermatophore y
which will be more fully described later.

FIG. 123.

FIG. 123. —Outline of the right side of the body of a male speci-
men of Cyclops tenuicornis, without the appendages, to show the repro-
ductive organs. (From Graber, Beitraye zur Kenntniss der Generations-
orr/ane der freilebenden Copepoden. Zeit. f. Wiss. Zool. xxxiii. Taf.
xxv., Fig. 1.)

L Testis. vd, t. The first or proximal region of the vas deferens.
vd. 2. The second or spermatophore-fonning region, vd. 3. The third
region, or receptacle of the spermatophore.

(iii.) The third region (Fig. 123, vd. 3) is a short, en-
larged pouch, the receptacle of the spermatophore, sepa-
rated by an abrupt constriction from the second region,
and opening externally on the posterior edge of the first
abdominal somite, under a small lid or flap (Fig. 124, h)
which carries three stout hairs projecting backwards from
its free edge. After a spermatophore has been formed in

232

HANDBOOK OF INVERTEBRATE ZOOLOGY.

the second region it passes into this receptacle, where it
remains until it is transferred to the body of the female.

3. The spermatophore. The seminal receptacle usually
contains a spermatophore ; but as this is gradually com-
pleted in this cavity, perfectly mature spcrmatophores are
the exception rather than the rule. The arrangement of
the parts of the spermatophore varies somewhat in differ-
ent species, but the following four structures are always
present : the sheath, the discharging bodies, the sperma-
tozoa, and the cement.

FK;. 124. — Diagrammatic view
of the left side of the first ab-
dominal somite of a male speci-
men of Cyclops tenuicornis, more
highly magnified, to show the
ripe spermatophore in the termi-
nal region of the vas dpfrn-n*.
(After Graber, Taf. xxv., Fig. 8).
<•'/. The enlarged terminal por-
tion of spermatophore receptacle
of the left vas deferens. sp. Sper-
matophore. It. Lid-like plate
which covers the external genital orifice at the lower edge of the posterior
end of the first abdominal somite, o. Wall of vas deferens. b. A mass
of cement inside the cavity of the duct. c. Cavity of the duct. d. Sper-
matophore sac. e. Spermatozoa, filling the anterior half of spermato-
phore. /. Discharging bodies filling the posterior end. g. Cement body
and anterior end.

(i.) The sheath, or spermatophore sac (Fig. 124, d) is a
delicate, transparent, oval pouch, which is secreted around
the spermatozoa in the second chamber of the vas deferens.
The sheath is not quite complete, since its inner or ante-
rior end is open.

(ii.) The discharging bodies (Fig. 124,/) form a trans-
parent mass, which, in some species, fills the posterior
closed end of the sac, as shown in the figure, but in other

ANATOMY AND METAMORPHOSIS OF CYCLOPS.

233

species it forms a layer just inside the sac, over the whole
spermatophore.

If a male with a ripe spermatophore be gently pressed
under a cover-glass, the wall of the sac may be ruptured
so that the contents may escape as shown in Fig. 125, and
the discharging bodies (c) may then be seen to be small,
transparent, highly refractive spherules, which soon absorb
water, swell, and disappear. When the ripe spermato-
phore is transferred from the reproduc-
tive organs of the male to the body of
the female, as described further on, the
contact with the water causes these
spherules to swell, and drive the other
contents of the spermatophore out of
the sac into the seminal receptacle of the
female.

FIG. 125. — Contents of a ripe spermatophore of
Cyclops tenuicornis, which has been ruptured by
pressure. (From Graber, Taf. xxv., Fig. 5.)

a. Cement, b. Spermatozoa, c. Discharging
bodies.

FIG. 125.

(iii.) The greater part of the cavity of the sac is filled
by the spermatozoa (Figs. 124, c; 125, h ; 126). When
forced out by pressure they will be seen to consist of an
oval sheath with an inner spiral thread. The spermatozoa
of Cyclops are motionless %

(iv.) The anterior end of the s'ac is usually occupied by
an adhesive plug, the cement (Figs. 124, g ; 125, a) ; but
in some species the cement occupies the central axis in-
stead of the anterior end.

4. If possible notice the manner in which the spermato-
phore is transferred to the vulva of the female, where it is

234 HANDBOOK OF INVERTEBRATE ZOOLOGY.

fastened by the cement, until the discharging bodies drive
the spermatozoa into the seminal receptacle. Males and
females may occasionally be found while copulating ; and
if they are examined with a lens, the male may be seen to
clasp the thoracic limbs or abdomen of the female with his
jointed antenna;, and then, bending up his body, deposit
a spermatophore upon the external median aperture of the
seminal receptacle. This speumatophore adheres to the
body of the female, and the spermatozoa are absorbed
into the gland, and each time that eggs are laid a sufficient
number pass up through the ducts already noticed to fer-
tilize them. It is probable that one impregnation serves
for the whole life of the female. At any rate, one connec-
tion with the male serves to fertilize several broods of

FIG. 126. — Spermatozoa of Cyclops tenuicornis,
highly magnified. (FYoin Graber, Taf. xxv., Fig. 2.)
FIG. 126.

Place two or three egg-bearing females in a large watch-
crystal full of water; cover this with another crystal, or
with a glass tumbler, and set it aside until the eggs hatch.
Then carefully examine the water around the edges of the
crystal for the very minute and active young. Having
found a specimen, catch it with a dipping-tube, and trans-
ferring it to a glass slide, examine it with a power of two
hundred and fifty to three hundred diameters.

VI. The .Xattjtl/ifx. Stage. The newly-hatched larva.
of a Copepod is known as Xauplius. It has an oval body
(Fig. 127), and three pairs of jointed locomotor append-
ages, and presents the following points for examination.

a. The middle of the ventral surface of the body is
occupied by a large oval labrum (Fig. 127, Z), through
which the opening of the mouth may be seen.

ANATOMY AND METAMORPHOSIS OF CYCLOPS.

235

b. Around the mouth the three pairs of .appendages are
arranged.

1. The first pair (-4), which become the first antennae
of the adult, are the smallest, and consist of three setose
joints.

FIG. 127.

FIG. 127. — Nauplius. of Canthocaniptus Staphylinus, magnified five
hundred and seventy-five diameters. (From Hoek, Ent. der Entomo-
straken. Niederl. Arch. IV.)

A. First antennae. An. Second antennae, a. Anus. en. Endopodite.
ex. Exopodite. L. Labrum. N. Mandible, o. Ocellus, s. Stomach.

2. The second pair (An), which become the second
antennae of the adult, are much larger, and are the main
organs of locomotion. Each consists of a large setose

236 HANDBOOK OF INVERTEBRATE ZOOLOGY.

protopodite, which carries a jointed exopodite (ex) and
endopodite (en). All the joints carry movable setae,
and the terminal joints also bear long plumose hairs.

3. The third pair of appendages (M) are much like
the second, and become the mandibles of the adult.

c. The dorsal surface is almost entirely covered by the
oval carapace, near the anterior margin of which is the
black^double eye-speck (o).

d. Posterior to the carapace is the last abdominal seg-
ment, which carries the anus («), and a pair of terminal
setae.

FIG. 128.

FIG. 128. — Young Cyclops, with two pairs of fully-developed thoracic
limbs, and a rudimentary third pair. (From Claus, in Bronn's Klassen
u. Ordnunyen tZe.s Tli'n m ichs. Arthropoda Taf. xiii., Fig. 6.)

a. Abdomen, c. Carapace, d. First antenna, e. Second antenna.
/. Mandible. </. First maxilla. //. Second maxilla. i. First thoracic
appendage, j. Second thoracic appendage, k. Rudimentary third tho-
racic appendage, t. Thoracic somites, o. Ocellus.

e. The digestive tract consists of : —

(i.) A short oesophagus, which runs upward and for-
ward from the lower surface of the labrum.

(ii.) The dark-colored stomach (.s-).

(iii.) The pear-shaped thick-walled intestine.
f. Upon each side of the stomach is a transparent cir-
cular tube, the shell-gland, which does not seem to be
furnished with an external opening.

HARD PARTS OF THE GRASSHOPPER. 237

g. After two or three moults the posterior end of the
body lengthens to form the long hind-body of the adult,
while the rounded anterior portion becomes the carapace
of the adult. The mandibles develop cutting blades upon
their basal joints, and the two pairs of maxillae make their
appearance as small buds on the ventral surface of the
body.

li. After one or two more moults, the second antenna
becomes uniramous, as shown in Fig. 128, e. The
blade (f) of the mandible becomes fully developed, and
the two terminal branches of the nauplius mandible dis-
appear. The two pairs of maxilla? (g, h) assume their
adult form, and the thoracic appendages («,./, &) and the
free somites of the thorax and abdomen appear, in succes-
sion, from in front backwards. The larva changes grad-
ually, through a number of moults, until the adult form is
reached.

XXIII. — THE HARD PARTS OF THE GRASS-
HOPPER.

(Acridium Americanum.)

THE following description was written from the above
species, which should if possible be procured for labora-
tory work, as its large size makes it an especially good
type for elementary work. Any other grasshopper may,
however, be used, or even a cricket, or a cockroach.
Fresh specimens, or those which have been preserved in
alcohol, will answer for examination. If the alcoholic
specimens are stiff and brittle they may be softened by
placing them in warm water for a few hours.

Examine a fresh or a preserved specimen, and notice the

238 HANDBOOK OF INVERTEBRATE ZOOLOGY.

long, narrow, laterally compressed body, which is divided
into three well-marked regions.

1. The head, which is flattened from before backwards,
and elongated vertically. It carries the eye, the antennae,
and the mouth-parts, and is movably joined, by a short
neck, to the second region of the body.

2. The thorax, which, with the head, constitutes the
anterior half of the body. On its lower surface it carries
the three pairs of legs, which increase in size from before
backwards, the third pair being much the largest. The
posterior portion of the dorsal surface of the thorax car-
ries the two pairs of wings.

3. The abdomen, which is a little longer than the head
and thorax together, is made up of a series of movable
segments without appendages.

4. The wings. The anterior pair of wings, which are
known as the tegmina, or wing covers, are about as long
as the body, beyond the posterior end of which they pro-
ject. They are narrow, and the anterior and posterior
margins are seen, when the wing is extended, to be nearly
parallel. When folded upon the body their outer faces
are vertical, with the anterior margin below, and the pos-
terior or internal edges in contact along the back, the left
slightly overlapping the right.

«. With a pair of forceps seize the lower edge of the
wing-cover, at about the middle, and gently expand it by
pulling it downwards and outwards until it is at right
angles to the body. Notice that the surface which was
exposed in the folded wing-cover is now uppermost, and
the edge which was below when folded -is now the anterior
edge or costal margin.

b. Remove one of the wing-covers for examination. It
is a thin, transparent, rather stiff plate of chitin, irregu-

HARD PARTS OF THE GRASSHOPPER. 239

larly marked with dark-brown pigment spots. It is
strengthened by a network of chitinous tubes, the " veins ";
of which there are five on each wing, diverging from
the proximal end of the wing, and giving rise to smaller
veins. These in turn divide into much smaller veinlets,
which inosculate with each other and divide the surface
of the wing into small irregular polygonal areas or "cells."

(i.) The vein nearest the anterior or costal margin of the
wing is the costal vein. It is undivided, and may be traced
for a little more than half the .length of the wing.

(ii.) The second very much larger vein is the sub-costal.
It gives rise to several large branches, the subdivisions of
which form the framework of the greater part of the
wing.

(iii.) The third or median is much smaller, and soon
divides into two branches of nearly equal size.

(iv.) The remaining pair, which are known as the sub-
median and internal, run close to and nearly parallel with
each other near the internal or posterior margin of the
wing.

c. The wmg is divided by the veins into three areas : —
(i.) The costal area forms the anterior edge of the wing,

and is bounded posteriorly by the costal vein.

(ii.) The median area is much the largest, and lies be-
tween the sub-costal and sub-median veins.

(iii.) The internal area is the free margin posterior to
the internal vein.

d. Make a sketch of the wing-cover, showing the above
points.

e. The second pair of wings are about equal to the first
in length, and wrhen the animal is at rest are folded up
under the latter. On the side from which the wing-cover
has been removed seize the dark-colored maririnal vein of

240 HANDBOOK OF INVERTEBRATE ZOOLOGY.

the second whig with a pair of forceps and extend it with
a gentle pull outwards and forwards. It is then seen to'
be a thin parchment-like membrane, with a stiff anterior
edge, which is nearly straight, while the rounded outer
and posterior margins are thin and flexible. When the
wing is fully extended its upper surface is convex, and
its anterior margin is rendered still more rigid by being
overlapped by the internal margin of the wing-cover.

The numerous radiating veins are
so arranged that their elasticity causes
the wing to fold upon itself like a
fan as soon as its margin is released.

FIG. 129. — Front view of head of grass-
hopper (Acridium Americanum). (Drawn
from nature by W. K. Brooks.)

o. Antenme. 6. Ocelli, c. Eyes, d, d, d. The

.,_^.._=_. frontal portion of the epicranium. e. Clypeus.

' in /• Suture across the clypeus. y, y. Labmm.
h. Suture across labrum. /. Gena. k. Tips of
maxillae. I. Tips of ligulue. m. Maxillary
palpus, n. Labial palpus, o. Mandibles.

5. The Legs. Remove and examine the large leaping-
leg of the side from which the wing-cover was taken. It
consists of five regions : —

a. The coxa, or basal division (Figs. 130, 8, and
132, cZ, cZ', cZ"), which is joined to the thorax.

b. A small division, the trochanter (Fig. 132, e, e', e"),
immovably joined to the distal dorsal portion of the
coxa.

In this species the trochanter is quite small and imper-
fectly separated from the coxa. In most other insects it
is more conspicuous, and it should be examined in a man-
tis, or in a beetle, for comparison with the grasshopper.

HARD PARTS OF THE GRASSHOPPER.

241

c. The femur ) a long, swollen, club-shaped segment
•(Figs. 130, 10, and 132, /, /,/"), which makes up
nearly half the length of the limb. When the animal is
at rest the femur of the third or leaping leg extends up-
wards and back wards, with its distal end above the dorsal
surface of the body, as in Fig. 139, Fern.

This joint contains the powerful leaping muscles, the
areas indicating the points of attachment of which are
visible externally.

FIG. 130.

FIG. 130. — Side view of head and prothorax of grasshopper ( Acridium
Americanum). (Drawn from nature by W. K. Brooks.)

a. Antenna, b. Ocellus, c. Eye. d, d. Epicranium. e. Clypeus.
y. Labrum. i. Gena. k. Maxilla. I. Labium. m. Maxillary palpus.
n. Labial palpus. o. Mandible. 1. Lateral portion of pronotum.
2. Dorsal portion of pronotum. 3. Prothoracic prescutum. 4- Protho-
racic scutum. 5. Prothoracic scutellum. 6. Prothoracic postscuiellum.
7. Prosternum. 8. Coxa of first leg. 10. Femur of first leg.

In the grasshoppers of this family, the Acridii, the well-
known musical sound is produced by rubbing the inner
rough surface of the femur across the ridges formed by the
veins of the wing-cover.

242 HANDBOOK OF INVERTEBRATE ZOOLOGY.

d. The Tibia; about equal to the femur in length, but
very slender and of uniform diameter (Fig. 139, t).
When at rest it extends downwuds and backwards, ;it an
acute angle, from the distal end of the femur, but in the
act of leaping it is thrown backwards and the limb
becomes straight.

e. The tarsus, or foot (Fig. 139, /r), is made up of
four movable pieces : —

(i.) The first and longest carries, upon its lower sur-
face, three soft pads, which, by their adhesion to foreign
bodies, serve as a point of resistance in leaping.

(ii.) The second joint is much shorter, and carries but
one pad.

(iii.) The third is long and slender, with two curved
pointed claws, the iinrjucs, between which is a concave
sucking disk, the fourth joint or pulvillus.

f. Note that the first and second pairs of legs are much
like the third, but much smaller, and meeting the body
at a different angle, to fit them for crawling instead of
leaping.

g. Make a sketch of the third leg, indicating the joints.
6. The head.

The outer or dorsal surface of the head consists of a
very broad and long frontal surface which looks forward,
and a much smaller and shorter dorsal occipital area.

a. The epicranium forms the covering of the dorsal
occipital area (Fig. 130, d'), and then becomes narrow
and runs downwards between the eyes and antennae to
about the middle of the frontal area, where it again
enlarges (Fig. 129, d, d, d), and ends below in a
prominent, straight, transverse suture. Along the middle
of the occipital area there is a faint line, much more pro-
nounced in the young than in the adult, which appears to

HARD PARTS OF THE GRASSHOPPER. 243

indicate that the epicranium is made by the fusion, along
the median line, of two originally separate pieces. Run-
ning across the narrow portion between the upper ends of
the eyes is an obscure ridge which separates the occipital
portion from the frontal, and may indicate the union of
two originally separate segments.

b. The large, projecting, oval, highly polished compound
eyes (Figs. 129 and 130, c-), are situated upon the upper
portion of the sides of the head. They are marked with
parallel vertical bands of brown pigment ; and with a lens
the many thousand hexagonal facets or cornea? of the com-
pound eye may be seen.

c. A little anterior to the upper margin of each of the
compound eyes is a convex oval area, in which the integu-
ment is so thin and transparent that the white subjacent
tissue may be seen. These spots are the ocelli (Fig.

129, 6). A third ocellus is situated between the antennae
on the median line of the epicranium.

d. Between the eye and the narrow frontal portion of
the epicranium is an oval area, the antennary fossa, in the
centre of which the basal joint of the antenna is fastened
by a flexible membrane, which admits of motion in all
directions. The antenna itself (Figs. 129 and 130, a)
is made up of a small basal joint and twenty-six movable
rings, Avhich gradually increase in length from the base to
the tip.

e. The lower straight edge of the epicranium articulates
with a wide, short plate, the clypeus (Figs. 129 and

130, e), the sides of which are deeply notched, and show
traces of a division (/) into two plates.

/. In front of this is the movable, flap-like labrum
(Figs. 129 and 130, g, g, g), the free edge of which is
deeply notched upon the median line. This notch is the

244

HANDBOOK OF INVEltTEBRATE ZOOLOGY.

remnant of the suture formed by the union of the halves
or paired appendages which the luhrum represents.

g. On the side of the head notice a suture which runs
from the lower anterior angle of the eye to the lower
margin of the epicranium, and separates the latter from
the large plate, the gena (Figs. 129 and 130, *), which
forms the side of the head, and terminates beloAv in a free
pointed edge.

h. Between the lower anterior edge of the gena and the
clypeus is a dark-colored area, the outer surface of the
basal portion of the mandible (Figs. 130, o, and 131, B).

i. Make drawings of the front and side views of the

head, showing all these
points.

Fm. 131. — Mouth-parts of
AcridiumAinericanum. (Drawn
from nature by W. K. Brooks. )

A. Anterior surface of the
labrum. e. Clypeus. <j. La-
brum. g'. Terminal bilobed
portion. h. Suture. B. An-
terior surface of mandible.
C. Posterior surface of maxilla.
ca. Cardo. at. Stipes. //*/<. .Max-
illary palp, la. Lacinia. r/f<.<ial-
ea. D. Posterior surface of
In I mu n. yu. Gula. SHI. Sub-
mentum. jxj. Palpiger. »i. Men-
turn. Iff. Ligula. n. Labial
palp. E. Metastoma.

k. Remove the head by cutting the soft integument of
the neck, and raise the labrum by its free edge and cut
it off. Under it note the large, black-tipped, toothed
mandibles (Figs. 130 o, and 131, B) meeting each
other upon the median line ; their outer ends running

HARD PARTS OF THE GRASSHOPPER. 245

backwards, to articulate with the lower anterior edge of
the gena, by a joint which allows them to move towards
and away from the median line, but in no other direction.

L On the nearly flat posterior aspect of the head
notice : —

(i.) The large occipital foramen, by which the cavity
of the head communicates with that of the neck. This
foramen is bounded above by the epicranium ; at the sides
by the gena, and below by a crescent-shaped sternal ele-
ment, the gula (Fig. 131, D, gu).

(ii.) Movably articulated with the lower straight edge
of the gula (Fig. 131, D, gu) is the labium or lower lip
(Fig. 131, D), formed by the union of a pair of append-
ages, which are immovably united, but exhibit, upon the
median line, traces of this union. The labium consists
of: —

(a.) A basal portion, the mentum (Fig. 131, D, m).

(b.) A pair of terminal apron-shaped pieces, convex
behind and concave in front, the two halves of the ligula
(Fig. 131, Z), Iff).

(c.) On each outer edge of the mentum is a small piece,
thepalpiger (Fig. 131, D,pg).

(d.} Upon this is the three-jointed labial palpus (Fig.
131, D, n).

(e.) Between the base of the mentum and the gula is a
small immovable piece, the submentum (sm).

m. Draw the posterior aspect of the head and labium.

n. Remove the gula and the labium, and expose the
posterior faces of the anterior mouth parts.

(i.) Notice, in the median line, a dark-colored, chitinous,
spiny pad, the metastorna or tongue (Fig. 131, E), which
forms the posterior boundary of the mouth. Pull it out
with the forceps, and note the rows of spines which cover
its anterior face.

246 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(ii.) Arching over the tongue and forming the anterior
boundary of the mouth are the black tips of the maxillce,
meeting upon the median line. Each maxilla (Fig.
131, (7) is made up of: —

(«.) A basal joint or cardo (ca), which is directed trans-
versely to the long axis of the head, and articulates with
the lower posterior edge of the gena.

(b.) The second joint, or stipes (*(), runs forward at
right angles to the cardo, and parallel to the long axis of
the head. It is movable towards and away from the
median line.

(e. ) The maxillary palpus (mp} is carried upon the outer
angle of the stipes, and is made up of three short and
three long joints.

(d.) The lacinia, the toothed, black-tipped, cutting por-
tion (la) of the maxilla, is carried upon the inner margin
of the distal end of the stipes.

(e.) The galea (ga), or soft brown spoon-shaped portion
of the maxilla is carried upon the outer angle of the stipes
and bends around in front of the lacinia.

(iii.) Make a sketch of the maxilla, indicating all the
joints.

7. The Thorax.

Remove the legs and wings in order to examine the
structure of the thorax and abdomen. The thorax is made
up of three segments, each of which carries a pair of* legs.
These three segments are known as the prothorax, meso-
thorax and metathorax.

a. The prothorax.

The sides and dorsal surface of this segment are covered
by a large sunbonnet-shaped piece, the pronotum (Fig.
1$0, 2~), which bears a slight resemblance to the carapace
of a crustacean, but does not, as in the latter, extend over
the head.

HARD PARTS OF THE GRASSHOPPER.

247

The dorsal portion of the pronotum is prolonged hack-
wards along the median line, and partially overlaps the
second division or mesothorax. The anterior portion of
the pronotum is crossed by three grooves or sutures, which
divide it into four immovably united areas.

(i.) The first of these, which forms the anterior margin
of the pronotum, is known as the prothoracic presculum
(Fig. 130, 3).

FIG. 132. — Ventral view of
the thoracic region of Acridium
Americanum. (Drawn from
nature by W. K. Brooks. )

a. Prosternum. a'. Median,
and a", lateral portions of me-
sosternuin. a"'. Median, and
aiv. lateral portion of meta-
sternum. av, ovi. First abdom-
inal sternum. avii. Second
abdominal sternum. b. Me-
dian spine of prosternum.

c. Prothoracic episternum.
c'. Mesothoracic episteruum.
c". Metathoracic episternum.

d. Prothoracic coxa. d'. Meso-
thoracic coxa. d". Metatho-
racic coxa. e. Prothoracic
trochanter. e'. Mesothoracic

trochanter. e". Metathoracic trochanter. /. Prothoracic femur, f. Me-
sotboracic femur. /' . Metathoracic femur.

(ii.) The second is the prothoracic scutum (4}.
(?ii.) The third is the prothoracic sculellum (5).
(rv.) The last is the prothoracic postftcufeUum (#).

b. The ventral portion of the prothorax is formed by a
slender movable sternum (Figs. 130, 7, and 132, a),
which connects the sides of the pronotum with each other.
On the median line it carries, in this species, a large hairy
club-shaped spine (Figs. 132, b, and 139, b). Near the

FIG. 132.

248 HANDBOOK OF INVERTEBRATE ZOOLOGY.

outer ends of the sternum are the fossae for the attachment
of the limbs.

c. llemove the first thoracic segment and make sketches
of the front and side aspects.

d. The mesothorax and metathorax are much more com-
plicated, and together with the first abdominal segment,
are soldered together into a firm-walled box.

(i.) The flattened ventral surface of this box is made up
of three pieces.

1. The mesosternum, which consists of an anterior
median portion (Fig. 132, «') and two nearly rectangular
posterior prolongations (a", a").

2. The metasternum; a somewhat larger plate, which
consists of an anterior square tongue (a'"} which fills the
space between the posterior horns of the mesosternum ;
and a large pentagonal portion (aiv), which is so placed
thut one of its angles points backward along the median
line.

3. The first abdominal sternum (av, avi) is mortised
into the posterior margin of the metasternum in nearly
the same way that the latter is joined to the preceding
sternum.

(ii.) In a ventral view of the thorax the lower ends of
the episterna (c, c', c") and the fossae for the articulation
of the legs are visible at the sides of the sterna.

1. Parallel with the anterior half of the mesosternum
are the lower ends of the mesothoracic episterna (c').

2. Parallel with the posterior half of the moso^ternurn
are the fossae of the second pair of legs. The inner bor-
ders of these fossae are not formed by the mesosternum
itself, but by slender horn-like backward prolongations of
the lower end of the episternum.

3. Parallel with the anterior half of the metasternum are

HARD PARTS OF THE GRASSHOPPER. 249

the lower ends of the metathoracic episterna (c"), separ-
ating the fossae of the second legs from those of the third,
and sending prolongations backwards to form the inner
margins of the latter

(iii.) Make a drawing of the ventral view of the thorax,
showing these points.

(iv.) In a side view of a thorax, from which the prono-
tum, wings and legs have been removed, the space above
the leg fossa is occupied by four rectangular pieces,
which slope obliquely upwards and forwards. The ante-
rior margin of each of these is marked by a dark stripe
or band of pigments, and the posterior margin by a light
stripe.

1. The first or most anterior piece is the mesothoracic
episternum. Its lower margin is prolonged downwards
and backwards, and forms the anterior and lower boundary
of the fossa of the second leg.

2. The second piece is the mesothoracic epimeron. Its
lower end forms the upper and posterior margin of the
leg fossa.

3. The third piece is the metathoracic episternum,

4. The fourth is the metathoracic epimeron.

5. Between the mesothoracic epimeron and metathoracic
episternum, just above the mesothoracic leg-fossa, is a
small oval aperture provided with a pair of lip-like chitin-
ous valves. This is the respiratory aperture or spiracle
of the metathoracic segment.

6. Along the upper margins of the episterna and epi-
mera are a few small irregular pieces, to which the wings
are articulated.

(v.) Make a drawing of the side view of the thorax,
showing these points.

(vi.) The dorsal surface of the mesothorax and mcta-

250 HANDBOOK OF INVERTEBRATE ZOOLOGY.

thorax is formed by two nearly square areas, which occupy
the space between the wings. They are soft and membra-
neous, and the pieces which compose them are not sharply
defined.

1. The anterior border of each is formed by a narrow
plate, the prescutum (Fig. 133, «).

2. Back of this is a large, convex, dark-colored, glisten-
ing surface, the scutum (6).

3. Behind the scutum is a membraneous piece upon the
median line, the scutellum (d).

a 4. The posterior margin is occu-

pied by a long, narrow, light-colored
piece, the post-scutellum (e).

Fio. 133. — Mesonotum, or dorsal surface of
Mesothorax (Acridium Americanum). (Drawn
from nature by W. K. Brooks. )

a. Prescutura. b. Scutum, d. Scutellum,
FIG. 133. e. Postscutellum. c. Patagium.

5. Outside the scutellum on each side is an irregular,
projecting, movable piece, thepatagium (c), to which the
wing is articulated.

(vii.) Make a sketch of the dorsal surface.

8. The Abdomen.

This is made up of a number of segments without
appendages, movable upon each other, and presenting
only slight differences. The typical number of abdominal
segments appears to be eleven, and in both sexes of the
grasshopper eleven terga are present, although only eight
sterna are visible in the female and nine in the male.

a. The first abdominal segment is somewhat different
from the others, and its sternal and tergal portions are
widely separated. The sternal portion is immovably

HARD PARTS OF THE GRASSHOPPER. 251

united to that of the metathorax, and has been already
described.

(i.) The tergum is soft, membraneous, and dark-colored
like those of the thorax, and is strongly crested in the
median line. Near its lower edges are a pair of large
apertures closed by membrane, the auditory organs. On
the anterior margin of this orifice is a much smaller open-
ing, the first abdominal spiracle.

b. The remaining abdominal segments are composed of
a narrow sternal portion and a much larger tergal portion.
The two sides of the tergum meet along the back to form
a ridge. Near the lower margin of each half of the ter-
gum are a couple of longitudinal furrows, the traces of the
sutures between the epimera and episterna. Near the
anterior angles of the episternal regions of the second,
third, fourth, fifth, sixth, seventh and eighth segments are
the openings of the spiracles.

As the structure of the terminal segments of the abdo-
men differs considerably, according to the sex of the
individual, both males and females should be studied and
compared with each other. The females are more abun-
dant than the males, and may be recognized by the presence
of the strong, blunt forceps-like ovipositor which forms
the posterior extremity of the body. As the male abdo-
men is the simplest it should be examined first.

9. The abdomen of the rnn1i\

a. In a ventral or a side view (Fig. 135) nine distinct
movable sterna ( 6* to 9* ) are visible ; they are nearly
equal in length and similar in shape.

(i.) Posterior to the ninth sternum (£*) the ventral
surface of the body is occupied by a large spoon-shaped
sub-genital plate (a), convex below and concave above.
The posterior margin of this plate (Fig. 134, a) is deeply
notched upon the median line.

252

JIANDBOOK OF INVERTEBRATE ZOOLOGY.

(ii.) Above this plate is a large chamber open behind
and at the sides, the genital chamber (Fig. 135, y).

(iii.) On the lower floor of this chamber, and therefore
on the upper surface of the sub-genital plate, is the male
reproductive orifice.

b. In a dorsal view (Fig. 134) the terga are substan-
tially alike as far as the eighth.

(i.) The eighth (8) is a little shorter
than the seventh.

(ii.) The ninth (Fig. 134, 9} is only
about one-fifth as long as the eighth, and
is immovably united to the tenth, a faintly
marked suture separating the two.

(iii.) On the median line the tenth
tergum (Fig. 134, 10) is very narrow,
but at the sides it is about as long as the
ninth. The posterior margin of the tenth
tergum is sharply defined.

FIG. 134. — Dorsal view of end of abdomen of
male Acridium Americanum. (Drawn from nature
by W. K. Brooks.)
FlG 134 For explanation of letters and figures see Fig. 136.

(iv.) The eleventh tergum (Fig. 134, 11) is a movable
shield-shaped plate upon the median dorsal surface. It is
about as long as the eighth, and it is divided into two
nearly equal portions by a faint tranverse suture. In
shape it is quite different from the other terga, and its
sides and posterior margin are free.

(v.) On each side of this plate the outline of the dorsal
surface of the body is completed by a setose movable plate
(Fig. 134, d), about as large as the eleventh tergum, the
cercus. This plate projects back from the lateral margin
of the tenth tergum, to which it is movably articulated.

HARD PARTS OF THE GRASSHOPPER.

253

(vi.) Projecting beyond the end of the eleventh ter-
gum the bilobed end of the ventral sub-genital plate (a)
is visible.

(vii.) Raise up the end of the eleventh tergum and
notice below it a pair of vertical plates (Figs. 134 and
135, 6), one on each side of the median line, the podical
plates. Between these plates is the anus, and below them
the genital chamber, already noticed.

FIG. 135.

PIG. 135. — Side view of tip of abdomen of male Acridium America-
num. (Drawn from nature by W. K. Brooks.)
For explanation of letters and figures see Fig. 137.

c. In a side view (Fig. 135) notice that from the second
to the eighth segment the sterna are equal in length to
the corresponding terga, and the constrictions between the
segments entirely surround the body.

(i.) The suture, which on the dorsal surface marks the
line between the ninth and the tenth terga, does not ex-
tend down onto the sides of the body, and the lower mar-
gins of these two terga form a single plate.

(ii.) Below this plate is the ninth sternum (Fig. 135, 9*),
as long as the area formed by the union of the ninth and
tenth terga.

254

HANDBOOK OF INVERTEBRATE ZOOLOGY.

(iii.) Running backwards from the posterior margin of
the tenth terguin is the flat cereus (Fig. 135, d).

(iv.) Above this a portion of the eleventh tergum (Fig.
135, 11} is visible.

(v.) Below and internal to the cereus is the podical
plate (Fig. 135, 6), triangular in a side view : and below
this the large sub-genital plate (Fig. 135, «), which is
joined to the ninth sternum.
10. The abdomen of the female,
a. In a ventral or side view (Fig. 137), notice : —
(i.) The first to the seventh sterna, like those of the
male.

(ii.) The eighth sternum (Fig. 137,
8*) is nearly twice as long as the
seventh, and forms the sub-genital
plate. Its posterior end is pointed,
curved upwards, and its extremity
(Figs. 139, 11*) lies between the
plates of the ovipositor.

FIG. 136. — Dorsal view of end of abdomen
of female Acridium Americanum. (Drawn
from nature by W. K. Brooks.)

Explanation of letters and figures for Figs.
134 and 136: —

7, 8, 9, 10, 11. Terga of the seventh to
eleventh abdominal somites. a. Male sub-
genital plate, b. Podical plates, c. Free end
of eleventh tergum. d. Cerci. e. Suture.
g. Dorsal plates of ovipositor. 7i. Ventral
plates of ovipositor, t. Central plates of ovi-
positor, or "egg-guides."

FIG. 136.

b. In a dorsal view (Fig. 136), notice : —
(i.) The first ten segments, substantially like those of
the male.

HARD PARTS OF THE GRASSHOPPER.

255

(ii.) The shield-shaped eleventh tergum (Figs. 136, IT)
is shorter and wider than in the male.

(iii.) On each side of it, at a little lower level, is the
triangular podical plate (Fig. 136, b), which is not ver-
tical, as in the male, but is so placed that its broad sur-
face is seen in a dorsal view.

(iv) . Above, or dorsal to the podical plates, are the cerci
(Fig. 136, d), much smaller than in the male, but attached
to the posterior margin of the tenth tergum.

(v.) As in the male, the anus is between the podical
plates, just below the eleventh tergum.

FIG. 137.

FIG. 137. — Side view of tip of female abdomen of Acridium Ameri-
canum. (Drawn from nature by W. K. Brooks.)

Explanation of letters and figures for Figs. 135 and 137.

7, 8, 9, 10, 11. Terga. 7*, 8*, 9*. Sterna, b, b'. Podical plates, c. Tip
of eleventh tergum. d. Cerci. a. Sub-genital plate. <j. Dorsal division
of ovipositor, h. Ventral division of ovipositor, i. Median division of
ovipositor, or " egg-guide." x. Spiracles, y. Reproductive aperture.

(vi.) The space between the podical plates above and
the sub-genital plate below is filled by the ovipositor, the
tip of which (Fig. 136, g, h~) projects some distance be-
yond the eleventh tergum.

c. In a side view (Fig. 137), the terga are substantially

256 HANDBOOK OF INVERTEBRATE ZOOLOGY.

like those of the male, but the small cerci (d) do not hide
any portion of the eleventh tergum (11), and more of the
surface of the podical plate (b) is visible than in the male.
The large genital chamber between the podical plates above
and the sub-genital plates below is entirely occupied by the
ovipositor (#, h, i).

d. The ovipositor : this consists of six movable pieces,
three on each side of the median line. These three por-
tions are a large superior or dorsal piece (Figs. 136 and
137, g). Fig. 139, op1) ; an equally large inferior or ven-
tral piece (Figs. 136 and 137, h; Fig. 139, op3); and
a short internal portion (Figs. 136 and 137. i\ Fig.
139, op2) between the bases of the superior and inferior
pieces.

(i.) In a surface view, the internal pieces are hidden by
the two superior and the two inferior pieces, which are so
arranged as to form a long sheath around the internal por-
tions which form the true ovipositor. Each of the four
pieces of the sheath is pointed posteriorly, and when the
pieces are folded together the four tips are in contact.
Running forward from the tip of each is a flattened,
slightly concave surface, which in the superior pieces
faces backward and upward, and in the inferior pieces
backward and downward.

During oviposition the four pieces are brought together,
and their tips forced into the ground. They are then sep-
arated, and their flattened surfaces force the earth away
on all sides, thus making a pit, into which the internal
pieces then guide the egg.

11. The metamorphosis of the abdomen.

Collect a number of very small, newly-hatched grass-
hoppers, to study the changes of the abdomen. The young,
at the time they leave the egg, are essentially like the

HARD PARTS OF THE GRASSHOPPER.

257

adult, but they have no wings, and the abdomen, in both
sexes, consists of eleven distinct terga (Fig. 138, A, 6,
7, 8, 9, 10, 11), and ten distinct sterna (Fig. 138) A, 61,
71, 8l, 9l, 101). At the tip of the abdomen there are a
pair of flattened podical plates (Fig. 138, A, b) and out-
side these a pair of long, slender cerci (Fig. 138, A, d).
In the female, two long, slender processes (Fig. 138, A, h),
soon make their appearance on the middle of the eighth

FIG. 138.

FIG. 138. — Development of ovipositor and abdominal segments of a
grasshopper (Locusta virridissima). From Dewitz. " Ban und Entwicke-
lung des Stachels, und der Legescheide einiger Hymenopteren und
ili-r 'jrilnen Heuschrecke." Zeit. f. Wiss. Zool. xxv. 1875. Taf. xii.
Figs. 6, and 7.

A. Ventral view of the abdominal segments of a young female
grasshopper; showing the six prominences, from the eighth and ninth
sterna, which are to become the parts of the ovipositor. B. The same a
little older. C. Side view of B. 5, 6, 7-11. Terga of the abdominal
segments. 5', 6', T-lff. Sterna of the abdominal segments. 6. The
podical plates, c. Tip of eleventh tergum. d. Cerci. g. Upper plates
of ovipositor, h. Lower plates of ovipositor, i. Central plates of ovi-
positor.

sternum. These lengthen rapidly, so as to cover up the
ninth and tenth sterna as shown in Fig. 138, B and (7,
and become the two ventral pieces of the ovipositor
(Fig. 139, qpi).

258 HANDBOOK OF INVERTEBRATE ZOOLOGY.

Four somewhat similar processes (Fig. 138, A, g, and i),
appear upon the surface of the ninth sternum. They are
arranged in a transverse row, and the outer ones <j, are
much larger than the inner ones, and soon lengthen to
become the dorsal plates of the ovipositor (Fig. 138, A,
and B, g\ Fig. 139, o,p), while the smaller median pro-
cesses (i), become the inner pieces or egg-guides (Fig.
139, op2). During these changes the ninth and tenth sterna
become entirely covered up and obscured, so that no traces
of them are present in the adult female, and the ventral
surface of the abdomen ends with the eighth sternum
(Fig. 137, £i; Fig. 139, 11*).

The terga of the ninth, tenth, and eleventh somites (Fig.
138, C, 9, 10, 11), persist, but their growth becomes re-
tarded, so that they are very much shorter in the adult
than those of the preceding somites, although they are of
about the same length in the young.

XXIV. THE INTERNAL STRUCTURE OF THE
GRASSHOPPER.

(Acridium Americanum.)

PIN the specimen down, under water, back uppermost,
passing the pins through the wings, and along the sides of
the thorax. With a pair of fine-pointed scissors cut
through the integument along the dorsal surface of the
abdomen, and carefully separate it from the underlying
muscles, and pin it out at the sides.

a. If it has not been destroyed by the incision, notice
the dorsal vessel, or heart, a delicate tube, which lies just
below the integument, on the dorsal surface of the
abdomen.

INTERNAL STRUCTURE OF THE GRASSHOPPER. 259

b. Below the integument is a layer of small flat muscles,
the abdominal muscles.

c. Cut away the integument of the thorax, and notice
the large alary muscles, which entirely till the dorsal por-
tion of the mesothorax and metathorax. The muscles of
the opposite sides of the body are sharply separated, and
a thin chitinous partition runs down from the constriction
between the mesothorax and metathorax, and separates the
muscles of the wing-covers from those of the wings ; and a
similar partition from the constriction between the meta-
thorax and first abdominal segment covers the posterior
faces of the wing muscles.

d. The space between the muscles of the abdomen and
the viscera is filled with a loose network of a light-colored
substance, the corpus adiposum.

e. Running imvards from the spiracles on the sides of
the thoracic and abdominal segments notice the tracheae,
rather tough transparent tubes, which divide into smaller
branches, which pass to the various organs of the body.

(i.) Remove a small portion of the corpus adiposum;
place it upon a glass slide, in a drop of water, gently cover
it, and examining it with a magnifying power of about
eighty diameters, notice the transparent branched tracheal
tubes which ramify through its substance. Notice the
spiral elastic fibre which is coiled around the wall of each
tracheal tube, and which, by its elasticity, tends to keep
the tube permanently open.

/. Near the dorsal surfaces of the posterior abdominal
segments, surrounded by the corpus adiposum and numer-
ous tracheae, is the long, light-colored, reproductive gland
(Fig. 139, o), which varies greatly in size and shape
according to the age and sex of the specimen.

g. The digestive organs. These are quite dark in color

INTERNAL STRUCTURE OF THE GRASSHOPPER. 261

FIG. 139. — Female specimen of Acridium Americanum, dissected to
show the digestive and reproductive organs, and the ventral nerve-chain.
(Drawn from nature by W. K. Brooks).

a. Antenna, a1, a-, a:!, a4, a5, the abdominal ganglia, b. Tooth car-
ried by the prosternum. c. Compound eye. d. Epicranium. e. Cly-
peus. /. Femur, fu. Furcula. <j. Labrum. ig. Ingluvies. il. Ilium.
in. Maxillary palpus, n. Labial palpus, o. Ovary, p. Podical plate.
(H>. Gastric coeca. mj>. Malpighian tubules. r. Rectum. s. Sper-
matheca. sa. Salivary glands. s<j. Gastric ganglia. t. Tibia.
t2, t3. Second and third thoracic ganglia, ty. Tegmen. tr. Tarsus.
op, op', op'1. Ovipositor, vn. Ventriculus. w. Whig. 1'. Prothoracic
prescutum. 1". Prothoracic scutum. 1'". Prothoracic scutellum.
1™. Prothoracic postscutellum. 2. Mesothoracic tergum. 3. Metatho-
racic tergum. ^-13. The ten abdominal terga. 1*-11*. The thoracic and
abdominal sterna.

and vary slightly in structure according to the genus.
The folio wing description is strictly true only of the genus
Acridium. In order to expose these organs, dissect away
the corpus adiposum, the wing muscles, and the dorsal
integument of the head.
They consist of : —

1. The oesophagus, a tough, dark-brown, cylindrical
tube, which runs up from the mouth, and then bends at
right angles and pusses into the thorax.

2. In the mesothorax the oesophagus gradually enlarges
to form ;i thick-walled pouch, the ingluvies or crop (Fig.
131), iy), which occupies the mesothoracic and metatho-
racic segments.

3. On the sides of the anterior end of the ingluvies are
the delicate, white, dendritic, salivary glands (Fig. 129, sa)
which communicate with two salivary ducts, one of which
runs forward on each side of the oesophagus into the head,
where they open into the cavity of the mouth.

4. In many insects the ingluvies is sharply separated by
a constriction from the next region or proventriculus, but
there is no abrupt division in Acridium, and the proven-

262 HANDBOOK OF INVERTEBRATE ZOOLOGY.

triculus, which lies over the figure 3* in Fig. 139, is not
sharply separated from the ingluvies.

5. Running back from the posterior end of the proven-
triculus to the seventh abdominal segment is a lar«-e cvlin-

D «/

drical pouch, the ventriculus (Fig. 139, vri). Its anterior
end is about as large as the posterior end of the proven-
triculus, and its posterior end is much smaller.

6. Surrounding the spot where these two chambers join
each other are sixteen transparent, cone-shaped pouches,
the gastric coeca (Fig. 139, pp), placed base to base in
such a way as to form a belt of eight fusiform pouches
around the digestive tract. If the trachea1 which bind
them to the digestive tract are dissected away, it will be
found that the pointed ends are free, eight of them running
forwards on the sides of the proventriculus and ei^ht
backwards on the ventriculus.

7. Occupying the seventh, eighth and ninth abdominal
segments is the ilium (Fig. 139, tl), much smaller than
the ventriculus, cylindrical, and abruptly constricted pos-
teriorly, where it joins the small intestine or colon.

8. Twisted around the ilium are great numbers of small
white tubes, the malpighian tubes (Fig. 139, m), which
open into the ilium where it joins the ventriculus.

9. The colon, or small intestine (Fig. 139, co), is a
delicate light-colored tube, which originates at the pos-
terior end of the ilium, and bends abruptly upwards
towards the dorsal surface, where it abruptly enlarges to
form —

10. The rectum (Fig. 139, ?•), a small white sacculated
pouch, which lies directly before the terga of the ninth
and tenth segments.

11. The rectum opens at the anus, which lies between
the bases of the podical plates, on the lower surface of
the eleventh tergum.

INTERNAL STRUCTURE OF THE GRASSHOPPER. 263

li. The reproductive organs.

1. The or dry (Fig. 131), o) is a long white gland, situ-
ated above the ventriculus and ilium. It is made up of two
sets of tubes or ovarioles, which are bound together into
a compact mass. When this mass is carefully examined
with a lens the two sets of tubes will be seen to run up-
wards, forwards and towards the median line.

(i.) Near the posterior end of the ovary these tubes
communicate with two delicate transparent oviducts, which
run down around the posterior end of the ilium to the
ventral surface of the body.

(ii.) Here they unite to form a single median tube, the
vagina, which opens externally upon the upper surface of
the sub-genital plate.

2. On the median line, between the internal plates of
the ovipositor, there is a second much smaller external
orifice, which communicates with a lonsr slender convoluted

7 O

tube, which opens into a small white pouch, the sper-
matheca (Fig. 139, s), which lies above the posterior end
of the vagina.

i. The nervous system.

1. On each side of the ingluvies notice a small white
stellate spot, the gastric ganglion (Fig. 139, sg), radiating
from which are a number of small nerves and a larger
commissure, which may be traced forwards into the head,
where it joins.

2. The supra-oesophageal ganglia, which are situated
between the eyes, in the upper surface of the osso-
phagus.

3. From them a pair of short commissures run down,
forming a collar around the O3sophagus, to the ventral
nerve chain. This consists of 'commissural fibres, with
the following ganglionic enlargements : —

264 HANDBOOK OF INVERTEBRATE ZOOLOGY.

4. A sub-cesophageal. ganglion, situated in the head,
and sending nerves to the mouth-parts.

5. One ganglion for each thoracic segment. In Fig.
139 the second and third of these ganglia lie above the

o o

letters t2 and /3, and the first is nearly over the letter b.

6. Five abdominal ganglia, one in the second, one in
the fourth, one in the fifth, one in the sixth, and one in
the seventh segment. In the figure these ganglia lie
above the letters a1, «2, «3, a4, and «5.

7. On each side of the nerve chain, in the second and
third thoracic and the first to seventh abdominal segments,
notice the apodemata orfurcuke (Fig. 131), fu) projections
from the sterna to support the nerve chain.

j. The auditory organs. In all the grasshoppers of
this family, the Acridii, the organs of hearing are situated
upon the sides of the first abdominal segment, and are
quite conspicuous externally. In order to examine them,
split the body of a grasshopper along the median line,
rarcfully remove all the viscera, muscles, tracheae, etc.,
from one half, and notice the flat, oval, semi-transparent
tympanum upon the side of the first abdominal segment.
Cut it out with a pair of fine-pointed scissors ; place it on
a watch-glass, cover it with water, and carefully dissect
away any trachea) which may adhere to its inner surface.
Examine it with a hand-lens or a low power of the micro-
scope, and notice : —

1. A thickened rim or bow (Fig. 140, a) which forms
the margin of three sides of the organ. This rim is simply
n greatly thickened portion of the ordinary chitinous
integument of the body.

2. The space inside the rim is occupied by the thin,
semi-transparent tympanum (&), which is also a pail of
the chitinous integument.

INTERNAL STRUCTURE OF THE GRASSHOPPER. 265

3. On that side which is not surrounded by the rim the
tympanum is continuous with the ordinary integument.

4. On this side notice the spiracle (cf), and, below this,
the auditory nerve (I) passing from the third thoracic
ganglion to the ear.

Fio. 140.

FIG. 140. — Left auditory organ of a grasshopper (Stenobothrus rufus),
viewed from within and magnified about ten diameters. This figure is a
combination of three of the figures given by Oscar Schmidt (Die Gehor-
organe der Heuschrecken, Arch. f. Mih. Anat. xi. 195, 1875).

a. Thickened margin of the tympanum, b. The tympanum, c. Mus-
cles, d. Spiracle, e. Cone-shaped prominence, g. Its lateral prolon-
gation, f/'. Thickened fold of the tympanum. /;. Tube leading to the
triangular chamber, k. Triangular chamber. L Small ganglion. I. Au-
ditory nerve, m. Auditory ganglion.

5. A number of small muscles (c, c) are attached to the
free ends of the run, and are so arranged that when they
are contracted the tension of the tympanum is diminished.

6. That side of the tympanum which is nearest the

266 HANDBOOK OF INVERTEBRATE ZOOLOGY.

spiracle is the thickest, and its inner face is covered by a
mass of spherical pigmented cells.

7 . Near the centre of the tympanum there is a much
thinner, nearly circular space, near the centre of which
there is a triangular chamber (&) or cavity hollowed out
in the substance of the tympanum.

8. From this chamber a tube (/t) runs towards the
spiracle, and opens internally near the letter i, from which
point the tube is continued for a short distance as an open
channel (c).

9. At e, near the end of this channel, the tympanum is
greatly thickened and folded upon itself so as to form a
hollow, cone-shaped prominence (e), which projects from
the inner surface of the tympanum, while its cavity opens
on the outer surface at g.

10. Below this prominence the tympanum is folded so
as to form a channel (<7!).

11. Soon after it enters the ear cavity the auditory
nerve (?) expands to form the bell-shaped auditory gan-
glion (m), which rests upon one side of the cone-shaped
prominence (e), and is also continued upwards and down-
wards around the prominence. Below the prominence the
ganglion gives rise to a small nerve, which passes into the
channel c, and then enlarges to form an accessory gan-
glion (/), and passes from this through the tube (h) to the
triangular chamber (&) , where it enlarges to form a small
triangular ganglion, which may be called the tympanic,
since it is entirely surrounded by the chitin of the tym-
panum, except at the point wheise the nerve joins it.

The microscopic structure of the ganglia appears to vary
somewhat in the different genera of the family. In Steno-
bothrus (according to Schmidt, Arch. f. Mik. Anat. xi.
195) fine fibres radiate from the tympanic ganglion and

INTERNAL STRUCTURE OF THE GRASSHOPPER. 267

pass out into tubular spaces in the tympanum, where they
terminate in small expansions, which appear to be the
parts of the apparatus which are directly affected by the
vibrations of the membrane. The microscopic structure
of the larger ganglion (m) has been investigated (Ranke,
Zeit. f. Wiss. Zool. xxxv. 1875, p. 143) in the genus
Acridium.

Fia. 141. — Auditory ganglion of
Acridium cerulescens, greatly magnified,
after Ranke (Beitrage zu der Lehre von
den Uebergangs-Sinnesorganen, Zeit. Z.
Wiss. Zool. xxv. 1875, p. 143).

B. The auditory nerve and ganglion.
a. External or peripheral face of the
ganglion. &. Transparent portion.

c. Pigmented portion. d. Auditory
nerve, e. Fusiform bodies. /. Their
stems, g. Layer of nuclei, h. Gan- c
glion cells. A. Termination of a nerve
fibre, very highly magnified, a. Fusi-
form body. b. Stem. c. Nucleus.

d. Fibre which connects it to the gan-
glion cell, e, f. Nerve fibre.

12. According to this author, when the fresh ganglion
is removed with needles from the surface of the tympanum
of a grasshopper which has just been killed, and is placed
in water on a slide and examined with a high power of the
microscope, it is seen to be a' bell-shaped structure (Fig.
141, B), in which are seen : —

a. The flattened peripheral surface (a), which normally
lies in contact with the»side of the cone-shaped promi-
nence (Fig. 140, e).

b. The opposite rounded end.

c. The auditory nerve (d, Fig. 141), in which are to be
seen : —

268 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(i.) The external sheath, with a few scattered nuclei
upon its inner surface.

(ii.) The nerve, made up of a number of parallel fibres.

(iii.) These fibres may be traced into the ganglion,
where they diverge from each other.

d. In the ganglion are : —

(i.) An outer transparent layer (£>).

(ii.) A more opaque pigmented portion (c).

e. In the transparent portion are a number of highly
refractive spindle-shaped bodies (e) with an outer rounded
and an inner pointed extremity.

(i.) From the pointed end a fine, transparent, highly
refractive fibre or rod (f) runs backwards, and may be
traced nearly to the opaque portion of the ganglion.

f. On the anterior or distal surface of the opaque por-
tion are a number of highly refractive oval bodies, the
nuclei (</), arranged in a single row.

g. Back of these the mass of the opaque portion (i) of
the ganglion is made up of crowded, spherical, somewhat
granular ganglion cells (/*), which are embedded in the
granular substance of the ganglia, so that their outlines
are not readily seen.

13. When the fresh ganglion is torn to pieces with
needles, and the fragments examined with a high power, —

a. The spindle (Fig. 14, A, a) is seen to be a sharply
defined body, made up of a transparent, highly refractive
outer layer and a central granular core.

b. The pointed end of the spindle is continuous with the
rod (6), and wherever the latter has been disturbed by
the needles it is bent abruptly at an angle, thus showing
that it is brittle and inflexible. The rod is transparent
throughout the greater part of its length.

c. The posterior or inner end of the rod is opaque,

GENERAL ANATOMY OF A LAMELLIBRANCH. 269

granular, and continuous with a thin layer of granular
protoplasm which invests the nucleus (e).

d. The latter is united by a short thread of granular
protoplasm (d) to a ganglion cell (e), from the opposite
end of which a nerve fibre (f) originates and runs down
into the auditory nerve, and so to the third thoracic gan-
glion of the central nerve cord.

XXV. THE GENERAL ANATOMY OF A LAMELLI-
BRANCH.

THE following description is strictly applicable only to
the fresh-water genus Anodonta, but any of the Unionidaj
may be used for laboratory work, or if these are not to
be had, the common long clam (Mya) or the round clam
(Venus) may be used instead. Mya and Venus may be
obtained of the fish-dealers in most of our cities, and Unio
and Anodonta may usually be found in abundance in most
ponds, lakes and streams. Either fresh or preserved
specimens may be used. The valves of the shell of a
living specimen are usually so tightly closed that some
difficulty may be found in opening them. The best plan
is to place them in warm water — about fifty-five or sixty
degrees centigrade — for a few minutes. The muscles
will then relax enough to allow the blade of a scalpel to
be introduced to cut their attachment to the inside of the
shell. After the specimen has been opened it should be
placed in a dish of water, or water and alcohol, and all
the dissecting should be performed while the specimen is
submerged. The addition of alcohol to the water is a
great help, since transparent parts are rendered opaque
and visible by it, and it also coagulates the slime which
covers the body, arid thus facilitates the work.

270

HANDBOOK OF INVERTEBRATE ZOOLOGY.

FIG. 142. — Anodonta with the left valve of the shell and most of the
left lobe of the mantle removed, to show the gills and abdomen. (Drawn
from nature by S. Garman. )

GENERAL ANATOMY OF A LAMELLIBRANCH. 271

Explanation of letters for Fig. 142 : —

A. Anterior end. P. Posterior end. D. Dorsal surface. V. Ventral
surface, a. Mantle, ab. Abdomen. 6. Foot. br. Branchial siphon.
cl. Cloacal siphon, d. Anterior adductor muscle, e. Posterior adductor
muscle. /. Posterior foot-retractor muscle, h. Anterior foot-retractor
muscle, hi. Hinge ligament. i<j. Inner gill of left side. Ip. Labial
palpi, mo. Mouth, oy. Outer gill of left side. s. Eight valve of shell.
u. Uinbo.

I. Examine first the outer surface of the shell and
notice : —

a. The two elongated irregularly oval pieces or valves
of the bivalve shell, one on each side of the body. Notice
the thin layer of horny-brown, or red or olive-green epider-
mis, which covers those parts of the shell which have not
been eroded.

b. On the surface of each valve the concentric lines of
growth.

c. Near the middle of one side of each valve, an area,
usually much eroded, around which the successive lines
of growth are arranged ; this, the oldest part of the shell,
is the umbo or beak (Fig. 142, u) and the margin upon
which it is situated the dorsal margin (Fig. 142, D).

d. Notice that the ventral margins of the valves, and
their ends, are free from each other, as well as the greater
portion of their dorsal margins.

e. Near the umbones they are united by the brown
horny hinge-ligament (Fig. 142, hi).

f. The ligament is posterior to the umbones, and thus
furnishes a means of distinguishing the somewhat pointed
posterior end of the shell (P) from the more regularly
rounded anterior end (A).

</. AVutch a living mussel in the water, and notice the
soft white margins of the mantle which protrude slightly
beyond the edges of the shell.

272 HANDBOOK OF INVERTEBRATE ZOOLOGY.

h. In some specimens the large white fleshy foot (Fig.
142, b) will be seen to project from between the anterior
ventral edges of the shell.

i. At the posterior end of the body the margins of the
mantle are so modified as to form two imperfect tubes
which project beyond the shell, the siphon tubes.

1. One of these, the cloaca! N/////O/, (Fig. 142, cZ), is on
the dorsal surface of the shell, between the ligament and
the posterior end.

2. The other or branchial siphon (Fig. 142, br) is at
the posterior end of the body, and its edges are set with a
fringe of small sensitive tentacles.

3. Fill a long slender glass tube with some colored sub-
stance, such as finely powdered carmine in water. Place
the lower end of the tube near the cloacal siphon, and
allow a few drops of the fluid to escape. It is violently
driven away from the mouth of the siphon. When the
coloring matter is allowed to escape near the lower or
branchial siphon it is sucked in, and in a short time some
of it is driven out through the upper or cloacal opening ;
thus showing that a continuous current of water, the bran-
chial current, is passing in at the one and out at the other
opening.

II. Before opening the specimen it is best to study the
inner surface of another shell, noticing : —

a. The large kidney-shaped scars for the attachment of
the two adductor muscles.

b. A line M'hich runs from the lower edge of the scar of
the anterior adductor along the ventral edge of the valve
to the scar of the posterior adductor. Thispallial line is
the area of attachment of the edge of the mantle to the
margin of the shell.

c. Above and in front of the scar of the posterior ad-

GENERAL ANATOMY OF A LAMELLIBRANCH. 273

ductor is a mucli smaller scar, the point of attachment of the
posterior retractor muscles of the foot, and near the scar of
the anterior adductor are two small marks, indicating the
points where the anterior foot retractors and the foot pro-
tractors are attached.

d. In the shell of Unio, notice the hinge teeth, which
are situated upon the thickened dorsal edges of the
valves.

1 . The anterior or cardinal teeth are situated under the
umbones, and are very irregular in shape. In most
species there is one in the right and two in the left valve.

2. Back of these and under the hinge ligament are the
long, narrow, lateral teeth; one in the right and two in the
left valve.

e. The shell is made up of three layers.

1. The horny epidermis which covers the outer surface
of the valves, and is reflected over their free edges into
the mantle.

This layer is directly continuous with the hinge liga-
ment.

2. The pearly layer which covers the greater portion of
the inner surface. When carefully examined with a lens
this layer is seen to be made up of very thin, flat, super-
imposed layers of pearl, the edges of which are visible
a.s line sinuous lines on the inner surface.

3. The darker prismatic layer is between these two,
and is exposed only along the edge of the inner surface.
When examined with a lens it is seen to be made up of
polygonal prisms, placed perpendicular to the surface of
the shell.

/. Examine a fractured surface with a hand-lens, and
notice these layers, as seen in section.

III. In order to expose the body, raise one valve of the

274 HANDBOOK OF INVERTEBRATE ZOOLOGY.

shell by separating the mantle from it along the pallial
line, with the handle of a scalpel, and then cutting the
two adductor muscles and the foot retractors. As soon as
these muscles are cut, notice that the elasticity of the
hinge ligament throws the ventral margins of the shells
apart. In the animal thus exposed, notice : — ,

a. The semi-transparent mantle (Fig. 142, a), which
lines the inner surface of the shell.

b. The thickened muscular margin.

c. The band of small mantle muscles which were at-
tached to the shell along the pallial line.

d. The adductor and retractor muscles.

e. Notice that the two lobes of the mantle are united
along the region of the hinge. Above the anterior ad-'
ductor they separate, and they are free from each other
along their anterior, ventral, and posterior margins as far
as the branchial siphon, which is simply an enlargement
of the narrow space between them. Above this opening
they unite to form the .lower edge of the cloacal siphon,
and they are then separated as far as the posterior end of
the hinge ligament.

/. On the dorsal surface of the body, a little anterior to
the posterior adductor, notice a region where the mantle
is quite thin and transparent — the pericardia! chamber.
Watch this chamber carefully, and notice through its Avail
the pulsating heart.

</. On the middle line of the upper posterior face of the
posterior adductor muscle, notice the small rectum (Figs.
143 and 144, m), which opens by the anus into the cloacal
siphon.

7^. Raise up the loose portion of the mantle, and notice
the large branchidl chamber into which the branchial siphon
opens. In this chamber notice : —

GENERAL ANATOMY OF A LAMELLIBRANCH.

275

FIG. 143.

FIG. 14.1 —Semi-diagrammatic view of Anodonta, seen from below
\vith the in,!"r gills separated from each other, to show the cloacal cham-
ber, the posterior adductor muscle and the floor of the organ of Bojanus.

a. Mantle. «l. Branchial Siphon. <///. Abdomen. />. Foot. bo. Ex-
ternal opening of the organ of Bojanus. c. Gills, e. Posterior adductor

276 HANDBOOK OF INVERTEBRATE ZOOLOGY.

. muscle, ex. Outer lamella of inner gill. i. Cerebral ganglia, in. Inner
lamella of inner gill. j. Cerebro-pedal commissure, k. Cerebro-visceral
commissure. /. Parieto-sphlancnic ganglia. lp. Labial palpi, m. Rec-
tum, mo. Mouth, pg. Pedal ganglia, t. Reproductive orifice.

1. The four long flat gills (Fig. 142, o, g, i, g ; Figs.
143 and 144, c), two on each side, which arc- attached to
other structures above, but hang down into the branchial
chamber, like longitudinal curtains, with their ventral
margins free.

2. Hanging down into the space between the gills is the
soft abdomen (Figs. 142 and 143, a, 6). Its walls are
muscular, and the anterior and posterior foot retractor
muscles form its anterior and posterior faces, and suspend
it between the valves of the shell.

3. On its ventral surface these muscles unite to form
the foot (Figs. 142, 143, and 144, />), which is usually
quite small in a specimen which has been opened, but
is capable of great extension, and usually protrudes in the
living animal from between the ventral edges of the shell.

4. Notice that the inner gill of each side is a little
larger than the outer, and its anterior edge rests between
a pair of flat, triangular, lip-like processes, the labial jialpx
(Figs. 142 and 143, ?,^).

5. Above the foot, and just below the anterior adductor
muscle, these palps are continued across the front of the
abdomen, and between them is the large oval opening of
the mouth (Figs. 142 and 143, m, o).

/. Pass a bristle into- the dorsal siphon and notice that
it lies above the gills, and does not pass into the branchial
chamber. Remove the animal from both valves of the
shell, and cut, with a pair of scissors, along the line where
the inner edges of the inner gills join each other. Spread
the specimen out, under water, as shown in Fig. 143 and

GENERAL ANATOMY OF A LAMELLIBRANCH. 277

notice that the bristle has passed into u chamber which is
dorsal to the gills, and which is known as the cloacal
chamber.

j. The gills. Notice that the upper edge of each gill
carries a row of openings which communicate with the
cloacal chamber. These are the openings of the vertical
water tubes. Pass a bristle into one of the water tubes,
and notice that this ends blindly at the free ventral edge
of the gill. Notice also that it is separated by vertical
partitions from the water tubes before and behind it.
"When the microscopic structure of the gill is studied as
described in Section XXVII. each water tube will be
seen to communicate with the branchial chamber through
a great number of microscopic ciliated openings, the bran-
chial slits, which cover the flat surfaces of the gill. The
water which is drawn through the branchial syphon into
the branchial chamber is driven by the cilia through the
branchial slits into the water tubes, and as these are filled
the water flows up into the cloacal chamber, and is dis-
charged from the body through the cloacal siphon.

1. Each of the four gills consists of two flat plates, the
outer and inner lamellae (Fig. 143, ex and in) , and these are
united to each other by vertical partitions, which separate
the water tubes from each other.

2. The upper edge of the outer lamella of each outer
gill is united to the mantle.

3. The upper edge of the inner lamella of the outer gill
is united to that of the outer lamella of the inner gill, and
the anterior third is also united to the wall of the abdomen.

4. The inner lamellae (e) of the inner gills are united to
each other for about one third of their length at the pos-
terior end of the body, but at the posterior end of the
abdomen they separate and pass one on each side of it.

278 HANDBOOK OF INVERTEBRATE ZOOLOGY.

In some sub-genera they are united to the abdomen from
this point to their anterior ends, but in Anodon and most
Unios they are free for a small part of their length, so that
there is a direct communication between the branchial and
cloacal chambers.

k. The Nervous System. After the gills have been
separated from each other, as described in i, the lower
surface of the posterior adductor muscle (Fig. 143, e) will
be seen near the posterior end of the body.

1. Near the anterior edge of the muscle a pair of
orange-brown masses, the parieto-splanchnic ganglia
(Fig. 143 and 144, /) will be seen, covered by a trans-
parent layer of integument. Carefully dissect this off, to
expose the ganglia and the nerves which run from them,
noticing : —

(i.) A nerve which runs backwards to the rectum (in).

(ii.) A pair of large pallial new?*, which run backwards
and outwards to innervate the edges of the mouth.

(iii.) A pair of large branchial y/rrws-, which run to the
gills.

(iv.) A number of small nerves, which run forwards
and outwards from the ganglion to adjacent parts.

(v.) Near the middle line a pair of much larger trunks,
the cerebro-visceral commissures (Figs. 143 and 144, k).
These can be traced forward for some distance, but more
anteriorly they pass into the substance of the abdomen
(«£>), and cannot be traced without dissection. Carefully
dissect them out as far as the anterior edge of the abdo-
men.

2. Each of them will be found to join a small cerebral
ganglion (Figs. 143 and 144, i) The two cerebral ganglia
lie at the sides of the mouth under the labial palpi. Each
gives rise to pallial nerves, which pass to the mouth ;

280 HANDBOOK OF INVERTEBRATE ZOOLOGY.

FIG. 144. — Anodonta cygnea, seen from the left side. The mantle
and gills of the left side, the labial palpi, part of the pericardium and
part of the organ of Bojanus have been removed. (From Rolleston,
Forms of Animal Life, Plate V. )

a. Right mantle lobe. a'. Branchial siphon, a". Dorsal edge of
mantle, b. Foot. c. Gills, d. Anterior adductor, e. Posterior adduc-
tor. /. Posterior foot-retractor, g. Foot-protractor, h. Anterior foot-
retractor, i. Cerebral ganglia, j. Cerebro-pedal commissure, j'. Audi-
tory organs. k. Cerebro-visceral commissure. /. Parieto-splanchnic
ganglia, m. Rectum, n. Heart, o. Pericardium, p. External opening
of organ of Bojanus. q. Channel of communication between its glandu-
lar and non-glandular portions, r. Opening between glandular portions,
s. Glandular portion, t. Reproductive orifice.

labial nerves which pass to the palpi, and to three commis-
sures.

(i.) One of these is the cerebro-visceral commissure,
which has just been traced.

(ii.) Another is the cerebral commissure, which passes
in front of and dorsal to the mouth, and joins the two
cerebral ganglia to each other.

(iii.) The third is the cerebro-pedal commissure (Figs.
143 and 144, /), which runs downwards along the anterior
edge of the abdomen, under the muscles.

3. In the foot these commissures bend 1 tack wards, and
join the pair of pedal ganglia (Fig. 143, pg). These two
ganglia are fused with each other on the median line, and
they are embedded in the muscles of the foot in such a
way that they cannot be found without careful dissection.
They are at some distance from the outer surface, and
very near the inner or abdominal surface of the foot.
They give rise to a number of nerves which pass to the
muscles of the foot.

4. If possible find a very young specimen of Unio or
Anodonta, one less than quarter of an inch long, and
having cut out the foot, place it upon a glass slide, and

GENERAL ANATOMY OF A LAMELLIBRANCH. 281

gently pressing it under a cover, examine it with a power
of about eighty diameters. Having found the pedal gan-
glion, search carefully for the auditory organs. These are
a pair of spherical microscopic pouches, each of which
contains a round, highly refractive calcareous ossicle.
After the auditory organ has been found in a small speci-
men, carefully dissect out the pedal ganglion of a full-
grown specimen under the microscope, and try to find the
auditory organs and the small nerves which join them to
the cerebro-pedal commissures. If a young Unio or
Anodonta cannot be found for microscopic examination,
any other very small marine or fresh-water lamellibranch
will answer.

m. The reproductive and renal openings. On each side
of the abdomen, above the cerebro- visceral commissure,
notice a small slit (Fig. 143, £), through which the repro-
ductive organs open into the ckmcal chamber, and just
above and close to these a second pair of openings (Fig.
143, bo), the external apertures of the renal organs, or
Oryans of Bojanus.

n. Open a fresh specimen, and remove the body from
the shell, exercising great care to avoid injuring the soft
parts. Place it in water with the dorsal surface above,
and notice on the middle line the transparent pericardium
(Fig. 144, o). Carefully open this, and notice that the
dark-colored intestine runs through it longitudinally.
The greater part of the cavity of the pericardium is occu-
pied by the transparent heart (Fig. 144, n), which con-
sists of a median ventricle wrapped around the intestine,
and two lateral auricles.

1 . The ventricle is a large oval transparent pouch which
gives rise to an anterior aorta dorsal to the intestine, and
a posterior aorta ventral to. the intestine.

282 HANDBOOK OF INVERTEBRATE ZOOLOGY.

2. On each side of the ventricle is a large transparent
auricle, which receives the blood from the bases of the
gills and drives it into the ventricle.

3. Carefully study the pulsation of the heart. The
auricles swell irregularly and become filled with the trans-
parent, colorless blood from the gills, and they then
contract, slowly and irregularly, while the ventricle
becomes distended. A slow wave of contraction then
runs from one end of the ventricle to the other, and forces
the blood into the aorta.

4. Notice that the pericardium is also filled with blood.

5. Open the ventricle, and notice the lip-like valves,
which prevent the blood from returning to the auricles.

0. The venous sinus and the renal organs.

Cut the intestine, and the auricles, so that they may be
removed from the pericardium, thus exposing its floor,
and the organs which lie below it.

1. The venous sinus is a long chamber, with a transpa-
rent roof, which lies along the middle line of the floor of
the pericardium, into the cavity of which it opens, near
its anterior end, by a single median aperture.

2. On each side of it is one of the renal organs, or
organs of Bqjanus. Each of these is a long tube, doubled
upon itself so as to form an upper and a lower chamber.
The upper chamber lias thin, transparent walls, and is
known as the non-glandular portion (Fig. 145, «'). Its
anterior end bends downward, and opens at / in Fig. 145,
into the cloacal chamber. The lower chamber has thick,
dark-colored, folded walls, and is known as the glandular
portion of the organ. At its anterior end it opens into
the cavity of the pericardium (Fig. 145, ?*'), at i. Ante-
riorly, the cavity of the non-glandular portion is separated
from that of the glandular portion, but posteriorly the two
communicate with each oilier.

GENERAL ANATOMY OF A LAMELLIBRANCH.

283

(i.) The opening from the pericardium into the glandu-
lar portion will be found at the anterior end of the former,
just below the point where the intestine enters it. Pass a
bristle through it, into the non-glandular portion.

(ii.) The non-glandular portion lies above and outside
of the glandular portion. Open it and find, at its ante-
rior end, the external opening into the cloacal chamber.
Notice, at its posterior end, its communication with the
dark-colored, thick-walled, glandular portion.

FIG. 145.

FIG. 145. — Diagram of Bojanus organ of Unio pictorum. (From
Bronn, Klassen und Ordnungen, Malacozoa. Tab. xxxii. Fig. 11.)

a. Glandular portion of organ of Bojanus. a'. Non-glandular portion.
L Opening from pericardium into glandular portion. I. External open-
ing of non-glandular portion, m. Reproductive orifice, n. Ventricle.
n1. Pericardium. L Rectum.

(iii.) Cut through the floor of the non-glandular portion,
and lay open the glandular portion. Notice the bristle
which has been passed into it from the pericardium.
Notice that the glandular portion runs back much further
than the non-glandular portion, and becomes expanded at
its posterior end to form a large pouch, which rests against
the posterior adductor muscle.

3. The blood from the various parts of the body finds
its way to the venous sinus, some of it passing through

284 HANDBOOK OF INVERTEBRATE ZOOLOGY.

the pericardium ; it then passes through the glandular
walls of the renal organs to the gills, and is then returned
to the auricles, to be again driven to the various organs of
the body.

p. The Digestive Organs. It is very difficult to trace
these in a fresh specimen, and one which has been hard-
ened in alcohol should therefore be used.

1. Notice the mouth, on the middle line of the body,
under the anterior adductor muscle, and between the labial
palpi.

2. Carefully dissect it out and trace it upwards to the
small, irregular stomach.

3. Around the stomach notice the compact, dark, brown
liver, which opens, by several irregular apertures, into the
stomach.

4. The intestine is a long, delicate tube, which is em-
bedded in the light-colored reproductive organs, which
form the greater part of the abdomen. It first runs
downwards from the stomach nearly to the foot ; then
upwards nearly to the dorsal surface ; then down again
nearly to the foot, where it bends forwards and then up-
wards to leave the abdomen and enter the pericardium.
It passes through the ventricle, and, leaving the pericar-
dium at its posterior end, passes over the posterior adduc-
tor muscle.

5. The posterior end of the intestine, or the rectum,
bends around the adductor muscle, to open at the anus
into the cloaca! chamber, close to its aperture, so that the
faeces are swept out of the mantle cavity by the current
of water from the gills.

q. The reproductive organs. These make up the greater
part of the substance of the abdomen, and are alike in
form in both sexes. They vary in size with the season,

EXAMINATION OF UNIO OR ANODONTA. 285

being large at the time of reproduction, and very small
immediately afterwards. They open into the cloacal
chamber, as already noticed.

When the eggs pass out of the ovary they are conveyed
into the water tubes of the outer gills, which serve as
brood pouches, in which the developing eggs and young
are carried.

XXVI. — THE EXAMINATION OF TRANSVERSE
SECTIONS OF UNIO OR ANODONTA.

THE general arrangement and relations of the parts in
Unio or Anodonta will be most easily understood by the
study of a series of transverse sections of a hardened
specimen.

The sections which are figured are from Unio purpurea,
but any species will answer.

An animal which has been preserved in strong alcohol
will 1>e found to be in fair condition for making sections,
but one which has been hardened in chromic acid is better.
The animal should be placed, alive, in its shell, in a quart
or more of one per cent chromic acid, and allowed to
remain for about forty-eight hours. After this time it
should be removed to seventy per cent alcohol, and al-
lowed to remain for a day or two. It may then be pre-
served in ninety per cent alcohol, and kept until it is
wanted.

In order to cut the sections, the body must be carefully
removed from the shell without cutting or breaking it.
This may be done by forcing the valves of the shell far
enough apart to introduce the handle of a scalpel, which
may be used to force away the mantle and muscles from
their attachment to the shell. The body may now be

286

HANDBOOK OF INVERTEBRATE ZOOLOGY.

placed in a basin of water, and sliced vertically ,with a
ra/or at intervals of half or one-third of an inch. The
sections should then be preserved for study under alcohol
in a shallow dish or saucer. The more instructive sections
are : one through the posterior portion of the posterior
adductor muscle ; one through the space between the pos-
terior adductor and the heart; one through the heart;
one through the middle of the abdomen ; and one through
the anterior portion of the abdomen.

I. A section through the posterior adductor muscle.
In this, as in all the other sections, two main chambers
or cavities are to be noticed.

a. The mantle cavity (Fig. 146, d, A), which is widely
open below, and contains the gills (Fig. 146, e,f).

b. Above this, notice the body
cavity, which in this section is
almost entirely filled by the ad-
ductor muscle (Fig. 146, g), the
rectum (Fig. 146, p), and con-
nective tissue.

FIG. 146. — Diagram of a vertical section
of the body of Unio purpurea in the region
of the posterior adductor muscle. (Drawn
from nature by W. K. Brooks. )

a, a. Mantle lobes. b. Glandular epi-
thelial layer of mantle, c. Dorsal lobes of
mantle. d. Cloacal chamber of mantle
cavity, e, e. Inner gills. /,/. Outer gills.
g. Posterior adductor muscle, li. Branchial
chamber, ft'. Dorsal portion of mantle
cavity, p. Rectum.

FIG. 146.

c. Above the intestine is what appears to be another
small cavity (Fig. 146, A'), but if the posterior end of the
section be examined, it will be found to be part of the

EXAMINATION OF UNIO OR ANODONTA. 287

mantle cavity, with which it is continuous, behind the
adductor muscle, so that a section of this region would
show a single cavity containing the gills, and open both
ventrally and dorsally.

d. The sides of the mantle cavity are formed by the
mantle lobes (Fig. 146, a, a), each of which is made up
of:-

1. An outer integument, or glandular epithelium, which
is normally in contact with the inside of the shell, and by
which the shell is excreted. •

2. An inner integument, or ciliated epithelium, which
faces inwards and lines the mantle cavity.

3. A loose network of muscular fibres and connective
tissue, which fills the space between these two layers.
(The embryology of the lamellibranchs, as well as the
study of sections, shows that this space is a part of the
body cavity, which has become filled with connective
tissue.)

e. If the two layers of integument be traced upwards,
they will be found to diverge in the upper part of the sec-
tion, the outer glandular layer passing over the surface of
the adductor muscle (Fig. 146, g), as a thin, transparent
pellicle (Fig. 146, b), the inner ciliated layer, on the con-
trary, is reflected inwards below the adductor muscle, and
thus forms the roof of the mantle cavity (Fig. 146, d).

The body cavity, with its contained organs, is thus en-
tirely surrounded by integument.

f. The body cavity.

This is comparatively unimportant in this section ; it
contains : —

1. The adductor muscle (Fig. 146, g).

2. The intestine (Fig. 146,^?), with its horseshoe-shaped
cavity and ventral ridge, which is mushroom-shaped when
seen in section.

288 HANDBOOK OF INVERTEBRATE ZOOLOGY.

3. If the section has passed through the parieto-
splanchnic ganglia, these will be seen between the lower
surface of the muscle and the roof of the mantle cavity,
upon the middle line.

g. The mantle cavity.

This contains the gills, and is divided by them into two
chambers.

1. The branchial chamber (Fig. 146, /<) , which is widely
open below, but is bounded at the sides by the mantle
lobes, and above by the gills.

2. The cloacal chamber (Fig. 146, d), which is bounded
above by the adductor muscle ; at the sides by the mantle,
and below by the gills.

h. The gills. The four gill plates (Fig. 146, e,f), are so
arranged as to form a double W, which separates the bran-
chial from the cloacal chamber.

1 . Note that the upper margin of the outer lamella of
the outer gill (f) of each side is united to the surface of
the mantle. It is important for a correct appreciation
of the homology of the mantle cavity among the lamelli-
branchs, to bear in mind the fact that this union of the
gills to the mantle is a character of secondary importance,
which is lacking in the young of Unio and Anodonta, and
in many adult lamellibranchs of other families.

2. The inner lamellae of the inner gills (e) of the two
sides of the body .are united to each other at cZ, but the
ridge thus formed is free dorsally.

3. The inner lamella of the outer gill of each side is
united to the outer lamella of the inner gill, and the ridge
thus formed is also free dorsally, and contains a small
blood-vessel.

i. Make a drawing of the section, showing all these
points.

EXAMINATION OF UNIO OR ANODONTA.

289

II. The examination of a section between the posterior
adductor muscle and the heart.

a. Notice the mantle cavity (Fig. 147, h, i, &), in sub-
stantially the same position as in the preceding section :
containing the gills (Fig.
147, I, m), and bounded
at the sides by the man-
tle lobes(a, a), andabove
by the body cavity.

FIG. 147. — Diagram of a
vertical section through the
body of Unio purpurea, be-
tween the heart and the
posterior adductor muscle.
(Drawn from nature by W. K.
Brooks. )

a, b, c, and h. as in Fig.
146. i, L Cloacal tubes of
outer gills. A;. Cloacal tube of
inner gills. I. Outer gills.
m. Inner gills. n. Outer
lamella of outer gill. o. In-
ner lamella of outer gill.
q. Outer lamella of inner gill.
r. Inner lamella of inner gill,
s. Retractor muscles of foot.
t. Glandular portion of organ
of Bojanus.

FIG. 147.

b. The body cavity is of about the same size as in the
previous section ; somewhat triangular in shape, and occu-
pying the dorsal portion of the section.

1. On the median line of the body cavity, close to the
dorsal surface, notice the intestine (Fig. 147, p), with
horseshoe-shaped cavity and ventral ridge.

(i.) The intestine is surrounded by a layer of connec-
tive tissue, which is united above to the dorsal portion of
the integument.

290 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(ii.) A thin plate of connective tissue may also be
traced downward below the intestine, as a sort of ventral
mesentery, which connects the intestine to the integument
of the roof of the mantle cavity, and thus divides the
body cavity into halves.

2. On each side of this mesentery, notice the sections
of the foot-retractor muscles (Fig. 147, s).

3. The remainder of the body cavity is filled, on each
side of the partition, by a dark-colored, glandular organ,
with very thick, delicate, plicated walls, enclosing an ir-
regular cavity (Fig. 147, t). This structure is the gland-
ular portion of the organ of Bojanus. Notice that the
halves of this organ are entirely separated by a partition.

4. The body cavity is limited below, as in the preced-
ing section, by the ciliated layer of the integument of
the mantle.

c. The mantle cavity.

This contains the gills, and is now divided, by the at-
tachment of the gills to the body, into four chambers
(Fig. 147, h, t, f, &)-

1. The lower or branchial chamber (h) presents sub-
stantially the same features as before.

2. The cloacal chamber (d, of Fig. 146), is now divided
into three chambers.

(i.) A central chamber (&) which lies above the two
inner gills, on the median line.

(ii.) Two lateral chambers (i, i) which lie above the
outer gills, and which may be called the cloacal tubes of
the outer gills.

d. The gills.

1. Note that the upper edge of the outer lamella (n) of
rach outer gill (I) is attached as before, to the mantle.

2. The inner lamellae (r) of the inner gills (m) are united
to each other, but not to the roof of the mantle cavity.

EXAMINATION OF UNIO OR ANODONTA. 291

3. The ridge formed by the union of the inner lamella (o)
of the outer gill (/) to the outer lamella (7) of the inner
gill (m) is now attached to the walls of the body cavity,
thus dividing the cloacal chamber into three parallel tubes,
which the previous section shows to be in communication
with each other posteriorly.

e. Make a drawing of the section, showing all these
points.

III. The examination of a section through the heart.

a. The mantle cavity is of substantially the same shape
as in the previous sections, but it is now divided into five
chambers (Fig. 148, //, i, i, k, k).

1. Of these the branchial chamber (h) is much the
largest, and it contains not only the gills, but also the
abdomen, which hangs suspended over the median line of
the roof of the mantle cavity.

2. The cloacal tubes (?) of the outer gills are substan-
tially as in the preceding section.

3. The median cloacal tube is now divided by the abdo-
men with two tubes (k, k) which may be called the cloacal
tubes of the inner gills.

b. The gills.

1. The outer lamellas of the outer gills are still attached
to the mantle, and the ridge formed by the union of the
inner lamella of the outer gill to the outer lamella of the
inner gill is attached to the roof of the mantle cavity.

2. The dorsal edge of the inner lamella of the inner
gill (m) is in this species free, so that the cloacal tube of
the inner gill is in communication with the branchial cham-
ber through the branchial slit. This is also the case in
Anodonta and in most of the Unionidse ; but in certain
sub-genera of the genus Unio there is no such slit, and the
inner lamella is in this region united to the integument of

292

HANDBOOK OF INVERTEBRATE ZOOLOGY.

the abdomen. The branchial slit is apparently for the
purpose of allowing the water which has passed through
the gills to pass back into the branchial chamber, and again

FIG. 148.

Fia. 148. — Diagram of a vertical section of Unio purpurea, passing
through the heart. (Drawn from nature by "W. K. Brooks.)

a to t. as in Fig. 146. w. Abdomen, r. Pericardium, w. Ventricle,
x. Auricles, y. Sinus venosus. z. Non-glandular portion of organ of
Bojanus.

through the gills, so that the branchial current need not be
interrupted when the animal is out of water, with its valves
closed ; this arrangement is of importance in such marine

EXAMINATION OF UNIO OR ANODONTA. 293

lamellibranchs as live above low tide mark, and are out
of water for some time every day.

c. The body cavity is now quite complicated and is
divided into several chambers, and contains the heart, in-
testine, sinus venosus, Bojanus organ, and reproductive
organs.

1. The larger portion of the body cavity is now occu-
pied by the cavity of the pericardium (Fig. 148, v), which
contains the heart and intestine.

2. The heart consists of a median ventricle (w) and two
lateral auricles (x) .

(i.) The ventricle is a delicate muscular cylinder, with
a large cavity, upon each side of which is the aperture of
communication with the auricle. This aperture is guarded
by a pair of flaps or lips, which project inward and meet
in front of the opening, and thus allow the entrance of the
blood, but prevent its return.

(ii.) On each side of the ventricle is a large muscular
auricle (x) with a small chamber, and thick spongy walls,
which are capable, during life, of very great distension.

(iii.) In this section the outer ends of the auricles are
united to the connective tissue of the body wall ; but in a
section a little anterior to this their cavities will be seen to
communicate with the blood vessels of the gills.

3. In the centre of the ventricle notice the cut section
of the intestine (p}, with its horse-shoe shaped cavity.

4. The space between the pericardium and the roof of
the mantle cavity is occupied by five chambers (Fig.
148, £, y, 2), one median and two pairs.

In the region through which this section has passed these
five chambers are entirely separated from the pericardium.

The median chamber (y) is the sinus venosus, and the
four others are the two non-glandular chambers (z), of the
organ of Bojanus, and its two glandular chambers (t).

294 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(i.) The sinus venosus. In the plane of this section this
is a small, delicate walled chamber (y), on the median line,
and its upper wall forms part of the floor of the pericar-
dium.

(a. ) Pass a bristle backward into the part of this cham-
ber which has been cut off posterior to this section. The
chamber will thus be found to end blindly behind.

(6.) Pass another bristle forward into the anterior part
of the chamber, which will be found to widen, and at its
anterior end an opening will be found through which its
cavity communicates with that of the pericardium.

(ii.) On each side of the sinus venosus are the sections
of the wide, flat, non-glandular, chambers of Bojanus (z).
Their upper walls form part of the floor of the pericar-
dium, and are thin and transparent.

(iii.) Below these, and meeting each other upon the
median line below the venous sinus, are the thick- walled
glandular chambers (t) of the organ of Bojanus.

(a.) Select the slice which has been cut off between
this section and the one next behind it, and pass a bristle
into this last chamber, and another into the non-glandular
chamber of the same side ; they will be found to pass out
together, thus showing that the glandular and non-glandular
chambers are in communication posteriorly.

(6.) Select the portion of the body anterior to this sec-
tion, and introduce bristles into the same chambers and
pass them as far forward as possible. No communication
between the two will be found, but it will be seen that the
non-glandular chamber does not lie above the glandular
throughout its whole length, but that their anterior ends are
side by side, and that each forms part of the floor of the
pericardium.

(c.) If care is used, the bristle which has been passed

EXAMINATION OF UNIO OR ANODONTA. 295

forward into the glandular chamber may be made to pass
through a small opening at its anterior end into the peri-
cardium.

(d.} The bristle which has been introduced into the
non-glandular part will, on the other hand, be found to
pass through an opening which communicates with the
cloacal chamber (&) of the inner gill.

5. The relations of these various chambers should also
be examined in more anterior sections, especially one just
anterior to the heart.

6. Suspended between the gills notice the large abdo.-
men (Fig. 148, u).

(i.) The wall of this organ is a whitish integument
which is composed of an external layer of epithelium and
an inner layer of muscular fibres.

(ii.) At the bottom or free end of the abdomen the
muscular fibres are more numerous, and form a muscular
foot. In the plane of this section the foot is quite small
or wanting, but further forward it is a conspicuous struc-
ture.

(iii.) The cavity of the abdomen is traversed in all
directions by a loose white network of connective tissue,
and the meshes of the network are almost entirely filled
by the white or brownish reproductive organs. In various
parts of different sections of the abdomen, sections of the
various folds of the intestine will also be seen.

7. Make a sketch of the section, showing the above
points.

IV. Sections through the middle and the anterior por-
tion of the abdomen should also be examined and sketched,
although they will be readily understood without explana-
tion.

1. In that through the middle of the abdomen the ex-

296 HANDBOOK OF INVERTEBRATE ZOOLOGY.

ternal apertures of the reproductive organs may be found,
although they are so small that the section is not likely to
pass through them. They are a pair of minute openings,
on the sides of the upper portion of the abdomen, and are
so placed that the reproductive elements are discharged
into the cloacal tubes of the inner gills.

2. In the section through the anterior part of the abdo-
men, notice : —

(i.) The dark green liver which lies on the top and left
side of the abdomen.

(ii.) The irregular cavity of the stomach, immediately
below and almost surrounded by the liver.

a. The large openings of the bile ducts, upon its sides.

(iii.) The large muscular foot, upon the free end of the
abdomen.

(iv. ) The pedal ganglia embedded in the muscles of the
foot on the median line.

XXVII. THE STRUCTURE OF THE LAMELLI-
BRANCHIATE GILL.

THE growing gills of an embryo and the simple gills of
such a form as Mytilus must be studied in order to
understand the highly complex gills of Unio or Anodonta.
In the embryo each gill is, at first, a row of tentacles,
growing out from the side of the abdomen into the mantle
cavity, and having their tips free in this cavity.

As Cyclas gives birth to jroung throughout the whole
spring and summer, embryos of this genus may be pro-
cured without difficulty for the study of the early stages
of the gill.

I. The examination of the gills of the Cyclas embryo.

The various species of this genus are small fresh-water

STRUCTURE OF THE LAMELLIBRANCHIATE GILL. 297

Lamellibranchs, from one-tenth to one-half an inch long.
They may often be found in abundance near the surface
of the mud at the bottoms of stagnant pools and ditches,
and sometimes in running water. They are also frequent-
ly found climbing upon various water plants. They may
be collected by washing the surface mud through the
meshes of a fine wire net or strainer.

If a full-grown Cyclas be carefully opened in a watch-
crystal full of water, its gills will usually be found to con-
tain from four to ten or twelve embryos in various stages
of development.

The largest embryos are very much like the adults in
structure, and their gills are fully formed. They are,
therefore, of no use for the present purpose, but they
should be carefully studied, as familiarity with their
appearance will facilitate
the search for smaller ones.

es.

FIG. 149. — View of right side
of a young Cyclas embryo, mag-
nified about two hundred diame-
ters. (Drawn from nature by W.
K. Brooks.)

s. The two valves of the cal-
careous shell, es. The embryonic
shell, m. The mantle, mo. The
mouth. /. The foot. g. The
pedal ganglia, rji. The gill ten-
tacles.

rrio

FIG. 149.

a. If one in which the two calcareous valves of the
shell have just made their appearance, as a pair of nearly
circular patches upon the sides of the embryo, be placed
upon a glass slide in a drop of water, and examined with
a microscope, the following points may be noticed : —

1. The large, projecting, ciliated foot (Fig. 149, /),
indicating the ventral surface of the animal.

298 HANDBOOK OF INVERTEBRATE ZOOLOGY.

2. About half way between the foot and the shell the
ventral border of the mantle is indicated by a horizontal
line or fold (Fig. 149, in) upon the side of the body.

3. Below the posterior portion of this ridge or fold,
notice that the body wall of the embryo is thrown into
undulations, so as to form a series of two, three or more
rounded prominences (Fig. 149, gi), the rudimentary gill
tentacles.

(i.) The epithelium of these prominences is continuous
with that of the general surface of the body, but much
thicker, and is made up of a single layer of large cells.

(ii.) Above the base of each tentacle notice a loose
mass of rounded mesoderm cells.

b. Find an embryo considerably more advanced, in
which the two valves have grown downwards so as to
cover up the abdomen and gills, and thus form a true
mantle cavity. Place it upon a slide in water, and ex-
amine the gills as they are seen through the side of the
transparent shell.

1. Each gill is now made up of a series of tentacles,
arranged side by side, but not united to each other ; their
ventral ends are free, and their dorsal ends are attached
to the side of the body.

2. The thick layer of epithelium which covers them
may be traced down one side of each tentacle to the tip,
then around and up on the other side to the point of
attachment, where it passes to the adjacent tentacle.

3. The outer surfaces of the tentacles are covered with
cilia.

4. Each tentacle is a hollow tube, closed below ; and
blood corpuscles may occasionally be seen in the cavities
of the tentacles.

II. The Gill of Mytilus.

STRUCTURE OF THE LAMELLIBRANCHIATE GELL. 299

The gill in such genera as Area, Mytilus, and Modiola
is about midway between the series of separate tentacles
of the Cyclas embryo and the continuous lamella of Unio
and Anodon, and enables us to understand how the latter
is formed by the union of a row of tentacles. The com-
mon marine Mussel, Mytilus edulis, may be found in
abundance attached by its byssus to piles and rocks near
low tide mark. The general form of the gills may be
studied in living or alcoholic specimens, but for making
sections to show the minute structure, the gills should be
carefully removed from the body and placed for twelve
hours in a three-tenths of one per cent solution of chromic
acid, and then transferred to seventy per cent alcohol ; after
they have remained in this for a day or two they may be
transferred to strong alcohol, ninety per cent, and kept
until they are wanted.

a. In an alcoholic specimen which has been carefully
opened note that, as in Unio or Anodon, there is an inner
and an outer gill upon each side of the body, and each
gill consists, as in Unio, of an inner and an outer
lamella.

1. As in Unio, the inner lamella (Fig. 150,6) of the
outer gill, and the outer lamella (c) of the inner gill are
united dorsally to each other and to the body wall.

2. The thickened ridge (z), formed by their union, con-
tains a blood-vessel (A1).

3. The outer lamella (a) of the outer gill, and the
inner lamella (d) of the inner gill, unlike those of Unio,
are free dorsally and end above in thickened ridges, which
also contain blood-tubes (&').

b. In a perfectly fresh living specimen, or in an alco-
holic specimen which has been carefully preserved 'and
opened, the surface of the gill is a broad, flat, vertically

300

HANDBOOK OF INVERTEBRATE ZOOLOGY.

striated plate suspended in the mantle cavity by its upper
margin, and terminating below in a continuous free edge.
When the gills are roughly handled in a living specimen,
or one which has died in pure water, or in many alcoholic
specimens, the lower edge of the lamella will be found to
fray out, or break up into a great number of fine threads,
and the gill now resembles a fringe rather than a flat plate.
In the uninjured living animal these threads will soon be
found to rearrange themselves in a continuous lamella,
somewhat in the same way that the
plumes of a ruffled feather soon
reassume their natural positions.

FIG. 150. — Diagram of the gills on one
side of the body of Mytilus edulis, magnified
about eight diameters. (Drawn from nature
by W. K. Brooks.)

o. Outer lamella of outer gill. b. Inner
lamella of outer gill. c. Outer lamella of inner
gill. d. Inner lamella of inner gill. e. Inter-
lamellar junctions. /. Cavity of tentacle,
shown only on the left side. h. Inter-ten-
tacular junctions, i. Line of attachment of
gills to body, k, k'. Blood channels.

FIG. 150.

1 . In an alcoholic specimen note that the threads or gill
tentacles which compose the outer gill are attached to the
body in such a way that their proximal portions make up
the inner lamella of the outer gill.

2. At the bottom or free edge of the gill each tentacle
bends outwards and upwards upon itself, so that its distal
half lies parallel to and near its proximal half. The dis-
tal portions of the tentacles make up the outer lamella of
the outer gill.

3. The gill tentacles of the inner gill are bent upon each

STRUCTURE OF THE LAMELLIBRANCHIATE GILL. 301

other, but in the opposite direction, and the proximal
halves of the tentacles here form the outer lamella, and
the distal halves the inner lamella.

4. The points of attachment of the gill tentacles to each
other.

(i.) All the tentacles of a gill are attached to each
other, and to the body along the line i.

(ii.) The distal ends of the tentacles are united to
form the ridge (&) which forms the dorsal margin of the
outer lamella of the inner gill, and of the inner lamella of
the outer gill.

(iii.) Each tentacle is very slightly united to the ad-
jacent tentacles by junctions which give Avay to the slight-
est strain, and which are represented diagrammatically
by the dots upon the right half of Fig. 150. These
points of union may be termed the inter-tentacular junc-
tions.

(iv.) Upon attempting to straighten a tentacle, the two
halves will be found to be fastened together by bands
which run from the inner to the outer lamella. These
bands, which may be called the inter-lamellar junctions
(Fig. 150, e), are formed by the meeting and fusion of
the walls of the two halves of the tentacle, which cannot
be separated without rupturing the connecting band.

( v. ) Each tentacle is hollow, and its cavity (Fig. 150,/"),
communicates with the longitudinal blood-vessels (&). At
the points of inter-lamellar junction, the cavity of the
descending portion of the tentacle communicates with that
of the ascending portion, as shown in the left side of
Fig. '150.

The resemblance between the embryonic gill of Cyclas
and that of the adult Mytilus will be readily perceived.
In each the gill is made up of a row of parallel tentacles,

302

HANDBOOK OF INVERTEBRATE ZOOLOGY.

attached by their proximal ends to the body wall. Myti-
lus differs from the Cyclas embryo in having the tentacles
bent upon themselves, so that their distal and proximal
halves are parallel, and side by side, and the two extremi-
ties near each other. Mytilus also differs from Cyclas in
having the distal ends of the tentacles united to each other,
as well as by the union of the
halves of the tentacle, through
inter-lamellar junctions, and also
by the slight adherence of adja-
cent tentacles by the inter-tentac-
ular junctions.

a, a

FIG. 151.

FIG. 151. — Surface view of four gill-
tentacles of Mytilus edulis, magnified one
hundred and fifty diameters. (Drawn from
nature by W. K. Brooks. )

a, a, a, a. Gill tentacles. b, b, 6, b. Inter-
tentacular junctions, c, c, c. Inter-tentac-
ular spaces. «7, d, d, d. Cavities of ten-
tacles.

c. Cut out a small piece of the unbroken gill of Mytilus,
and mount it in glycerine or balsam, in order to examine
its surface with a low power ; note : —

1. The gill tentacles, running side by side from the
dorsal margin to the ventral.

2. A series of lines at right angles to the tentacles, and
much farther apart, the lines of inter-tentacular junction.

3. With a higher power, notice the cavities of the ten-
tacles (Fig. 151, a, a, a, a), and the inter-tentacular
spaces (c, c, c).

4. Notice that the wall of the tentacle becomes thick-
ened at intervals (b, 6, 6, £>), thus giving rise to project-
ing pads upon the sides of the tentacle.

STRUCTURE OF THE LAMELLIBRANCHIATE GILL. 303

5. These pads are covered with large cilia which are
hooked at their free ends, and the hooks upon the pads
of adjacent tentacles interlock, thus forming the inter-
tentacular junctions.

6. Since the ciliated junctions of the opposite sides of
the tentacle are opposite each other, a line of junction
extends along the surface of the gill, at right angles to
the tentacles, and the surface of the gill is thus made up
of a rectangular grating, the vertical sides of the openings
being formed by the tentacles, and the horizontal ends by
the junctions.

7. The spaces thus bounded (c, c, c) are the incur-
rent ostia, through which water passes into the space
between the lamellae.

8. Draw the tentacles, as seen in a surface view.

d. Embed a portion of a gill which has been hardened
in chromic acid, and cut out and mount a number of
transverse sections. Examine these with a high power.

1. Examine a section which has passed through the free
portion of the tentacles, that is the portion which is not
attached to adjacent tentacles either by inter-tentacular or
inter-lamellar junctions.

(i.) The tentacle, when thus seen in section, is shaped
somewhat like the sole of a human foot (Fig. 152, «', a')
and consists of a central cavity (e) and a wall of epi-
thelium.

(a.) The layer of epithelium is thin over the sides and
inner surface of the tentacle, but the free end, that which
forms the outer surface of the lamella, is covered with a
thick layer of large cells.

(6.) These cells carry four bunches of large cilia (d, d)
which project over the space (c) between the tentacles,
and in the living animal cause the branchial currents in
the water which bathes the gills.

304

HANDBOOK OF INVERTEBRATE ZOOLOGY.

(c.) The cavity of the tentacle is lined by a chitinous
sheath (/).

(d.) Within this sheath the cavity is irregularly divided
by branching processes of connective tissue, within which
a granular white blood-corpuscle may occasionally be
found.

2. Make a drawing showing these points.

3. Examine a section which has passed through the
inter-tentacular, but not through the inter-lamellar junc-
tions (Fig. 152, a, a).

FIG. 152. — Transverse section of
four gill-tentacles of Mytilus, as seen
in a transverse section of the two la-
mellfe of a gill-plate. The section cuts
two tentacles of one lamella (the upper
in the figure) through the area of the
tentacular junctions ; the lower tentacles
are cut between the tentacular junctions.
(From " The Minute Structure of the
Gills of Lamellibranch Mollusca," by
R. llolman Peck. Quar. Jour. Mic.
Science, LXV., Jan. 1875.)

a, a. Sections through the inter-ten-
tacular junctions of two tentacles of the
outer lamella, a', a'. Sections of two
tentacles of the inner gill, between the
inter-tentacular junctions. b, b. The
bent cilia of the inter-tentacular junc-
tions, c. Space between the tentacles.
d. Tufts of cilia upon the outer edges of the tentacles, e, e, e, e. Cavities
of the tentacles. /, /. Chitinous lining of this cavity, g. Blood-
corpuscles within, this cavity.

(i.) Notice the cavity, the chitinous sheath, the exter-
nal epithelium, and the tufts of cilia, as in the preceding
section.

(ii.) Notice also twTo pads (b, b) upon the sides of
the tentacle, formed by the thickening of the epithelium,
and carrying large hooked cilia.

FIG. 152.

STRUCTURE OF THE LAMELLIBRANCHIATE GILL. 305

(iii.) Notice that the hooks of adjacent tentacles inter-
lock to form the inter-tentacular junctions.

(iv.) Draw the section.

4. Examine a section which has cut the inter-lamellar
junctions. (Fig. 153.)

(i.) Notice that the inner ends of the outer and inner
halves of each tentacle are united (Fig. 153, A), and the
cavities (e, e) of the two sides are continuous across
the neck (£), thus formed.

(ii.) The chitinous linings of
the two divisions of the tentacle
line only the outer ends of this
cavity (/), and do not extend
into the central portion.

(iii.) Draw the section.

FIG. 153. — Transverse section of four
gill-tentacles of Mytilus, through the inter-
tentacular and inter-lamellar junctions.
(From Peck.)

A, B, C, D, E, F, and G. as before.
H. Inter-lamellar junction. J. Cavity
of the inter-lamellar junction, continuous

with the tentacular cavity E.

FIG. 153.

III. The Gill of Unio.

Remove the gills from one side of the body by cutting
their attachments to the mantle and body ; place them in
water for examination. Each of the four gills is now seen
to be a flat plate, with a nearly straight dorsal margin by
which it is attached to the body, and a slightly curved
ventral margin, which is free.

a. Examine the dorsal margin of one of the gills, and
note that it is made up of two parallel plates, the two
lamella?, which are united at intervals by cross partitions,
the inter-lamellar junctions.

306 HANDBOOK OF INVERTEBRATE ZOOLOGY.

b. Introduce a small tube into the space between two
of these partitions, and force air or water into the cavity.
Notice that this fills a narrow space, which runs from the
dorsal to the ventral margin, where it ends blindly. The
air does not escape laterally, thus proving that the inter-
lamellar partitions reach from top to bottom of the gill,
and divide its cavity into a number of parallel vertical
chambers, the water tubes, which are closed below, open
above, and separated from each other.

c. On the side or face of the gill notice the fine parallel
lines, which run from the dorsal to the ventral edge.
These are the gill tentacles.

d. Notice also a second set of vertical lines, much far-
ther apart than the finer lines ; these indicate the edges of
the inter-lamellar partitions.

e. Cut out a small piece of the gill ; place it on a glass
slide ; cover it with water, and with a pair of fine forceps
tear away the lamella which is uppermost, and thus expose
the inner surface. Wash the portion which remains upon
the slide, and then stretch it thoroughly with needles, and
examine it with a low magnifying power (fifty to one hun-
dred diameters).

1. In a surface view notice the parallel, brown, torn
edges of the inter-lamellar partitions, and between them
the more transparent spaces of the water tubes.

2. Select a part of the specimen where the partitions
are somewhat Avidely separated, and focus a little deeper,
thus bringing the inner surface of the wall of the water
tube into view. Notice the irregular, scattered, somewhat
oval openings, the inner ends of the inhalent ostia, through
which the water gains access to the cavity of the wrater
tube.

3. Focus still deeper, so as to bring the external surface

STRUCTURE OF THE LAMELLIBRANCHIATE GILL. 307

into view. Notice the dark lines, more numerous than,
but parallel to, the partitions. These are the gill tentacles.

(i.) Crossing these at right angles, and two or three
times as far apart, a number of parallel, brownish, gran-
ular lines, the inter-tentacular junctions.

(ii.) In each of the meshes of the rectangular grating
which is formed by the intersection of these two sets of
lines, notice a rectangular aperture with rounded ends,
the external opening of the inhalent ostium.

(iii.) Note, by focusing up and down, that each of these
is continuous with one of the irregular openings already
noticed.

f. Make sketches showing these points.

g. Turn the specimen over to examine its external sur-
face ; wash and stretch it as before, and examine it with a
low power.

1. Notice the fine parallel vertical lines, the edges of
the gill tentacles.

2. Between the tentacles are vertical channels or gut-
ters, each of which is covered by two rows of large and
very active cilia, which project from the edges of the ten-
tacles, and meet over the grooves.

3. Place a little finely divided carmine upon the speci-
men, and notice the ciliary currents along the furrows.

h. Wash the specimen ; gently cover it with a glass
cover, and examine it with a high power.'

1. Focus so as to bring the outer surface into view, and
notice the rows of cilia along the edges of the tentacles.

2. Focus a little deeper, and notice the double row of
chitinous rods inside each tentacle.

3. Running across the spaces between the tentacles are
the fibrous inter-tentacular junctions.

4. Between the tentacles are the apertures of the inha-
lent ostia, situated at the bottoms of the furrows.

308

HANDBOOK OF INVERTEBRATE ZOOLOGY.

5. Focusing a little deeper, notice that each tentacle 13
a tube, with a cavity which is irregularly divided by con-
nective tissue fibres, among which white blood-corpuscles
may occasionally be found.

4. In order to gain a clear conception of the relations
of the parts of the gill, it is necessary to study sections
of hardened specimens. The more important points are
readily shown in sections of gills which have been placed,
for twelve hours, in a three-tenths of one per cent solution
of chromic acid ; and the hardened gills may be preserved
in ninety per cent alcohol.

a. Examine a transverse section, that is, one across the
water tubes, with a low power. Note : —

1. The two lamella (B and C, Fig. 154) , bound together
at intervals by the inter-lamellar partitions (^7, E, £J).

2. The water tubes (A, A, A).

FIG. 154. — Transverse section of the gill of Unio purpurea, magnified
eighty diameters. (Drawn from nature l>y \V. K. Brooks.)

A, A. Water-tubes. B. Outer lamella. C. Inner lamella. D. Blood-
vessels. E. Inter-lamellar partitions. F. Inhalent ostia. y. Gill-ten-
tacles.

3. In some of the partitions, the cut sections of blood-
vessels (D, D).

4. The outer surface of each lamella is seen to be folded
or corrugated, thus forming a series of rounded promi-
nences (6r, G, G), the sections of the gill-tentacles.

5. Between these tentacles are the furrows, which vary

STRUCTURE OF THE LAMELLIBRANCHIATE GILL. 309

in depth, some being quite shallow, while others (F, F),
open into the water cavity.

b. Make a sketch of the section.

c. Examine a portion of the section with a higher
power, two hundred and fifty diameters, noticing : —

1. The nearly oval cross sections of the external mar-
gins of the gill tentacles (Fig. 155, (7, g, g.)

2. The narrow necks by which these are joined to the
body of the lamella (?•).

FIG. 155.

Fro. 155. — Transverse section of a portion of the gill of Unio pur-
purea, magnified two hundred and fifty diameters. (Drawn from nature
by W. K. Brooks. )

a. Inter-lamellar water-tube, c. Outer lamella. /. Inhalent ostium.
g. Gill-tentacles, h. Their cilia, k. Their cavities. L Chitinous rods,
o. Inter-tentaculartfurrows. p. Epithelial lining of water-tube, p'. Epi-
thelial lining of inhalent ostium. r. Lamella.

3. The cross sections of the channels (o, o, o) between
the tentacles.

4. Some of these channels will be found to penetrate
the whole thickness of the lamella, as at f, thus opening
into the water tube (« ).

310 HANDBOOK OF INVERTEBRATE ZOOLOGY.

5. Notice that the layer of epithelium which lines the
water tube (p) may he traced outwards at (p') until it
becomes continuous with that which covers the exposed
edges of the tentacles.

6. The epithelium of the tentacles is greatly thickened,
and is made up of a single layer of large cells, which carry
the cilia (//, h) which project over the channels between
the tentacles.

7. Behind this thickened epithelium is the somewhat
triangular cavity of the tentacle (&).

8. On the sides of this cavity are the cross sections of
the chitinous rods (I).

9. Back of these rods is the narrow neck connecting the
tentacle with the body of the lamella.

10. The cavity of this neck is traversed in different
directions by scattered irregular connective tissue fibres,
not shown in the diagram, between which blood-corpuscles
will occasionally be found.

11. The space (r) is occupied by a network of branched
connective tissue, through which the blood finds its
way.

d. Make a drawing of the section, showing all these
points.

(iv.) A comparison of the gills of the Cyclas embryo,
of Mytilus, and of- Unio, shows that in all of them the
gills are made up of a series of parallel tentacles, bent
upon themselves to form the two lamellae, and that the
inter-lamellar and inter-tentacular junctions, which are
slight in Mytilus, are in Unio so much developed as to
bind the tentacles into a continuous organ.

The gill partitions of Unio are thus seen to be homol-
ogous with the inter-lamellar junctions of the two halves
of a tentacle of Mytilus. The adjacent tentacles of Unio,

THE DEVELOPMENT OF LAMELLIBRANCHS. 311

instead of being loosely attached to each other at intervals,
as in the inter-tentacular junctions of Mytilus, are fused
together to form a continuous lamella.

XXVIII. THE DEVELOPMENT OF LAMELLI-
BRANCHS.

AMONG the Unionidse the spawning season is very short,
and the early changes of the egg take place so rapidly
that it is rather difficult to find them for study ; and as
the later stages in the fresh-water forms are very aber^
rant, it is best for the beginner to study one of the more
typical salt-water forms. The spawning season is short
with them also, but it comes at different times in different
species, and the examination of a number of forms will
usually result in the discovery of sexually mature speci-
mens of some species at almost any time during the sum-
mer months. When the reproductive elements are ripe,
or nearly so, the abdomen is more or less distended by the
reproductive organs, and the student can therefore judge
what form to select for experiment. The method of
artificial fertilization, which is described in Section XIV.,
is to be employed, but it is much more difficult to obtain
perfectly ripe reproductive elements than it is with the
sea-urchin ; and the student should not be discouraged by
repeated failures.

I. The Fertilization of the Eggs.

Having obtained and opened a number of specimens of
a species which seems favorable, examine the contents of
the reproductive organs in the following manner, in order
to find the most perfectly ripe individuals.

If the point of a knife be pushed into the reproductive
organ a milk-like fluid will ooze out of the cut, and a little

312

HANDBOOK OF INVERTEBRATE ZOOLOGY.

of it may be taken upon a knife-blade and transferred to a
glass slide for examination. The drop of fluid should be
thoroughly mixed with a drop of sea-water and placed on
the slide, and gently covered with a cover-glass, and ex-
amined with a magnifying power of about one hundred
diameters. If the specimen is a female, this power will
show that the fluid is almost entirely made up of irregular
pear-shaped ovarian eggs (Fig. 156), each of which con-
tains a large circular transparent germinative vesicle sur-
rounded by a layer of granular slightly opaque yolk. It
is almost impossible to describe the slight differences
which distinguish the perfectly ripe egg from those which
are nearly ripe but not capable of fertilization ; although a

very little experience will
enable one to tell whether
it is worth while to attempt
the fertilization of the eggs
of any given female.

FIG. 150-172. — The embryology
of the oyster. (All the figures
were drawn from nature by W. K.
Brooks, and unless the contrary Is
stated they are magnified two hun-
dred and fifty diameters. )

FIG. 15C>. — Eggs from the ovary
of a ripe female, magnified one hun-
dred diameters.

FIG. 156.

When the drop of fluid is thoroughly mixed with the
sou-water, the eggs should appear clean, sharply defined,
separate from each other, and pretty uniformly distributed
through the drop, as shown in the figure. If they adhere
to each other, or if their outlines are indistinct, or if there
is much fine granular matter scattered between the eggs,
it is probable that the attempt at artificial fertilization will
at best be only partially successful.

THE DEVELOPMENT OF LAMELLIBRANCHS.

313

When a perfectly ripe female is found, it should be set
aside and the search continued for a male. When a drop
of the milky fluid from a ripe male is mixed with a little
sea-water and examined with a magnifying power of one
hundred diameters, it is seen at a glance to be quite dif-
ferent from the fluid of a female. There are no large

bodies like the eggs, but the fluid is filled with innumer-
able numbers of minute granules (Fig. 157), which are so
small that they are barely visible when magnified one
hundred diameters. They are not uniformly distributed,
but are much more numerous at some points ihan at
others, and for this reason the fluid has a cloudy or curdled
appearance. By selecting a place where the gran tiles are
few and pretty well scattered, very careful watching will
show that each of them has a lively dancing motion, and
examination with a power of
five hundred diameters will
show that each of them is tad-
pole-shaped (Fig. 158), and
consists of a small, oval, sharply
defined "head" and a long,
delicate- " tail," by the lashing
of which the dancing is pro-
duced.

FIG. 157. — Ripe seminal fluid, mag-
nified one hundred diameters.

FIG. 157.

It is more difficult to decide whether the male cells are
perfectly ripe than it is to decide in the case of the eggs.
With a magnifying power of five hundred diameters, each
"head" should have a clear, well-marked outline, and
they should be very uniform in size and separated from
each other, as in Fig. 158. Under very favorable circum-

314 HANDBOOK OF INVERTEBRATE ZOOLOGY.

stances this power should also show the " tails," as very
faint undulating lines.

If the " heads " vary much in size, or if they are aggre-
gated into bunches, with the " tails " radiating from the
bunches in all directions, or if there is much granular mat-
ter so small that the outlines of the particles are not visible
when magnified five hundred diameters,
the fluid is not perfectly ripe, and fertiliza-
tion with it will not, in all probability, be
very successful.

FIG. 158. — A portion of Fig. 157 magnified five
FIG. 168. hundred diameters.

As the male cells are infinitely more numerous than the
eggs, the ripe fluid from even one small male is enough to
fertilize all the eggs of five or six large females.

In order to fertilize the eggs, all that is necessary is the
mixture of the ripe eggs with a little of the ripe male fluid
in a drop of water. If the point of a knife-blade be
dipped in the fluid from a female and touched to a glass
slide, and then dipped into the fluid of a male and touched
to the same part of the slide, and a drop of sea-water be
added, to cause the two to meet, most of the eggs will be
fertilized, and their early stages of development can be
studied in a single drop of water, but to secure the fertili-
zation and healthy development of great numbers of eggs,
several precautions must be observed, and a few instru-
ments and pieces of apparatus are needed.

The following is a list of the things needed for procur-
ing, fertilizing and hatching the eggs : A pair of sharp-
pointed scissors ; a pair of small forceps ; half a dozen
watch-crystals; a set of about half a dozen glass beakers,
or tumblers, of different sizes, from half a pint up to half

THE DEVELOPMENT OF LAMELLIBRANCHS. 315

a gallon ; two or three dipping-tubes, or glass tubes six
or eight inches long, open at both ends, but with one end
drawn out to a fine point ; a small glass or rubber siphon
for drawing the water out of the beakers. For tracing the
development *of the eggs, a microscope, magnifying at
least one hundred diameters, and half a dozen glass slides
and thin glass covers are wanted.

After the specimens have been opened, and at least one
ripe male and one ripe female found, cut off the mantle
lobes and gills of the male with the scissors, close to the
visceral mass, and tear them out with the forceps and
throw them away. Cut around the adductor muscle with
the scissors, so that the visceral mass may be lifted out of
the shell and transferred to a small saucer or to a watch-
crystal. Holding the visceral mass with the forceps, cut
out with the scissors as much as possible of the digestive
organs and liver, and throw them away, and then chop up
the reproductive organs with the scissors, picking out and
throwing away any fragments of the liver, digestive organs,
mantle or gills which may present themselves. In order
to have the young thrive, the water must be kept free from
fragments of the various organs of the adult, as these
would soon decay and destroy the embryos, and it is there-
fore important to remove them as completely as possible.
After the mass has been chopped up as fine as possible,
fill up the watch-crystal with fresh sea-water, stir it up,
and then allow it to run into one of the smallest beakers,
which has been nearly filled with sea-water. As the
water runs out of the watch-crystal, be careful to allow as
few of the fragments as possible to run with it.

Now fill up the watch-crystal Avith water again, and stir
and pour off as before, and repeat the process until nearly
all of the male fluid has been washed out of the fragments

316 HANDBOOK OF INVERTEBRATE ZOOLOGY.

and poured into the beaker. Stir the contents of the
beaker for a short time, and then allow it to stand about
five minutes, to allow any fragments to settle to the bot-
tom, then pour the fluid, which should be quite milky,
into another small beaker, leaving behind, to be thrown
away, any particles which may have settled to the bottom.
The male cells retain their full vitality for several hours
after they have been mixed with sea-water, so the beaker
may be set aside to wait until the eggs an- ready. The
eggs swell up and break to pieces within a very few
minutes after they are mixed with water, unless the}' are
fertilized at once, so it is much better to add the eggs to
a previously prepared mixture of male cells and water than
it is to put the eggs into the water to wait until the male
fluid is got ready.

Taking now one of the females, remove and chop up the
ovary in the same way in another watch-crystal, observing
the same precautions in removing all portions of the body.
Fill the watch-glass with water, and stir and pour off into
the beaker as before, giving the contents of the beaker a
good stirring after each lot of eggs is added, in order to
diffuse them through the water at once, and thus ensure
the speedy contact of each of them with some of the
male cells.

Fill the ciystal with water again, and stir and pour off,
and repeat until all the eggs have been washed out of the
fragments of the ovary.

Another female may now be cut up, and the eggs may
be added to the contents of the same beaker, but if the
females are large, and yield many eggs, it is not best to
use more than one, for although there are enough male
cells to fertilize a very great number of eggs, the eggs are
heavier than water and soon sink to the bottom, and if

THE DEVELOPMENT OF LAMELLIBRANCHS. 317

they form a very thick layer, only those which lie near the
surface have room to develop.

The beaker should now be allowed to stand for about
ten minutes, and in the meantime some of the eggs may
be picked out with a dipping-tube for examination under
the microscope. In using the dipping-tube, cover the
' large end with the tip of the finger, and run the small end
down close to the bottom of the beaker, and then take the
finger off the top, and as the water runs in at the bottom
it will carry some of the eggs with it. When the tube is
filled, place the finger on the top again, and draw it out of
the water, and, holding it perpendicularly on the centre of
a glass slide, and taking the finger off the top, allow a
good-sized drop to run out into the slide.

If things are working properly, each egg should now
have a number of male cells attached by their heads to its
outer surface, with their tails radiating from it in all direc-
tions, as shown in Fig. 159, and cover-
ing it in such numbers that the lashinjr

of their tails causes the egg to rotate
and move through the water.

Fio. 159. — Egg about two minutes after fer-
tilization; showing the irregular outline, the
large genninative vesicle, and the spermatozoa,
attached to the surface of the egg. FIG. 159.

As soon as all the eggs have male cells attached to them,
it is necessary to get rid of the superfluous male fluid, for
it would soon decay and pollute the water if it were allowed
to remain, and if it is not drawn off from the eggs while
they are at the bottom, it is almost impossible to remove
it after the embryos have begun to swim, without losing
them as well.

318 HANDBOOK OF INVERTEBRATE ZOOLOGY.

After a final stirring, the beaker should be allowed to
stand for about five minutes, to allovy the eggs to settle to
the bottom, and the fluid above them should then be drawn
off through a siphon, reaching nearly but not quite down
to the eggs. A fresh supply of sea-water should then be
added, and the eggs being stirred and allowed to settle,
the water should be drawn off as before, and this should
be repeated until the water, after the eggs have settled to
the bottom, remains clear.

The beaker may now be set aside where it will ifot be
exposed to sudden changes of temperature, and the eggs
will require no further attention until the embryos beiriu
to swim. The little embryos must of course be supplied
with fresh sea-water from time to time during their devel-
opment, and as they are so small that the water cannot be
drawn off after they begin to swim, they must be supplied
with fresh water by transferring them from time to time
to larger and larger beakers. In two hours or so after the
eggs are fertilized the embryos of the oyster begin to
swim, .and crowd to the surface of the Avater in great num-
bers, and form a thin stratum close to the surface. This
layer of embryos may be carefully siphoned off into a
very small beaker, and a little fresh sea-water added. In
an hour or so there will be a new layer of embryos at the
surface of beaker No. 1, and these should also be siphoned
into No. 2, and this should be repeated as long as the
embryos continue to rise to the surface of the first beaker.
Every five or six hours a little fresh sea-water should be
poured from a height of a foot or more into beaker \o. 2,
until it is filled. The contents should then be poured into
a larger beaker, and sea-water should be added four or
five times a day as before. In this way the embryos may
be kept alive for a week, although they have by this time

THE DEVELOPMENT OF LAMELLIBRANCHS. 319

got into such a large vessel that it is almost impossible to
find any of them for microscopic examination.

II. The segmentation and development of the egg.

The following description has been written from the
eggs of the oyster, but it will be found
to apply pretty exactly, except as regards
time, to the developing eggs of other lamelli-
branchs.

FIG. 100. — Egg about thirty minutes after fertiliza-
tion. FIG. 160.

About fifteen minutes after the eggs are fertilized, they
will be found to be covered with male cells, as shown in
Fig. 159. In about an hour the egg will be found to have
changed its shape and appearance. It is now nearly
spherical, as shoAvn in Fig. 160, and the germinative ve-
sicle is no longer visible. The male cells may or may not
still be visible upon the outer surface. In a short time, a
little transparent point makes its appearance on the sur-
face of the egg, and increases in size, and soon forms a
little projecting transparent knob, — the polar globule, or

direction cell, — which is shown in Fig.

161, and in succeeding figures.

FIG. 161. — Egg two hours and eighteen min-
utes after fertilization; drawn with the formative
pole of the principal axis at the top of the
figure.

a. Macromere. 6. Anterior micromere. c. POST
FIG. 161. terior micromere.

Recent investigations tend to show that while these
changes are taking place, one of the male cells penetrates
the protoplasm of the egg, and unites with the germina-

320 HANDBOOK OF INVERTEBRATE ZOOLOGY.

tive vesicle, which does not disappear, but divides into
two parts, one of which is pushed out of the egg, and
becomes the polar globule, while the other remains behind
and becomes the nucleus of the developing egg, but
changes its appearance so that it is no longer conspicuous.
The egg now becomes pear-shaped, with the polar globule
at the broad end of the pear, and this end soon divides
into two parts, so that the egg (Fig. 161) is now made of
one large mass and two .slightly smaller ones, with the
polar globule between them.

The later history of the egg shows that at this early
stage the egg is not perfectly homogeneous, but that the
protoplasm which is to give rise to
certain organs of the body has separ-

/y i 1.

^ ° ated from that which is to give rise
to others.

FIG. 162. — The same egg, ten minutes later,
in the same position.
FIG. 162. Letters as in Fig. 161.

If the egg in the stage shown in Fig. 161, were split in
the plane of the paper, we should have what is to become
one half of the body in one part and the other half in the
other. The single spherule at the small end of the pear,
the macromere (a), is to give rise to the cells of the digestive
tract of the adult, and to those organs which are to be
derived from it, while the two spherules at the small end,
the micromeres (b and c), are to form the cells of the outer
wall of the body and the organs which are derived from it,
such as the gills, the lips and the mantle, and they are also
to give rise to the shell. The upper portion of the egg in
this and succeeding figures is to become the ventral sur-
face of the adult oyster, and the surface which is on the

THE DEVELOPMENT OF LAMELLIBRANCHS.

321

right side in Fig. 161, is to become the anterior end of the
body of the adult. The figure therefore shows the half
of the egg which is to become the left half of the body.
In most lamellibranchs, and especially in Unio and Ano-
donta, the micromere (6), is hardly distinguishable from
the macromere («), and the egg, at this stage, is like Fig.
162, instead of like Fig. 161.

In the oyster, this first stage of active segmentation is
followed, as it is in the sea-urchin, by a period of rest, dur-
ing which the divisions between the spherules (a, b, and c),
become almost obliterated. In Unio and Anodonta, and
in most marine lamellibranchs, the resting stages are hardly
recognizable, and the egg passes almost immediately from
one stage of segmentation to another, but in the oyster
the resting stages are well marked. The oyster egg, in
the first resting stage, is shown in Fig. 162. The macro-
mere («), and the anterior
micromere (6), are so com-
pletely fused with each other
that the line of separation is
invisible, while that which
separates the posterior micro-
mere (c), from the rest of the
egg is still distinguishable.

FIG. 163. — The same egg, ten
minutes later.

a, b, and 'c. as in Fig. 161.
d, d. The new microuieres. FIG. 163.

During the next stage of segmentation, the two micro-
meres (Fig. 163, b and c), again become sharply defined,
and each of them divides into two, so that we now have one
macromere («), and four micromeres (6, c, d, d). In Unio,

322 HANDBOOK OF INVERTEBRATE ZOOLOGY.

Anodonta, and many marine lamellibranchs, the spherule
(6) , at this stage, is not constricted oft' from a. This period
of activity is followed in the oyster by a second resting
stage, and the micromeres then divide by repented fusion
into a cap of small ectoderm cells (Fig. 164, ec), which
almost completely covers the macromere (a). At the same
time the direction cell is carried towards the anterior end
of the egg. Fig. 104 shows the oyster egg
about six hours after fertilization.

FIG. 164. — The same egg, seven hours and eight
minutes later.

a. Macromere. b. Micromeres. ec. Ectoderm.
g. Point where orifice of invagination is to be formed.

In about thirty hours after fertilization, the macromere
of the oyster egg also begins to divide into smaller cells,
and forms the digestive Layer, or endoderm. In about
thirty-six hours (Fig. 165), it becomes flattened, dorsally
and ventrally ; the endoderm (en), becomes pushed in
on one of the flat sides to form a saucer-shaped digestive
cavity with a wide mouth, the orifice of invagination (g);
a segmentation cavity is visible between the endoderm, and
the ectoderm (ec), and a few short cilia appear on the
outer surface of the ectoderm. In from thirty-six to forty-
eight hours, the oyster embryo assumes the form shown
in Fig. 166. A tuft of cilia, the velum (v), is developed
at the anterior end of the body, and the direction cell may
frequently be seen among the bases of the cilia. The
embryo now begins to swim actively, and finds its way to
the surface of the water. An optical section (Fig. 167, 6),
will show that this embryo is the flattened embryo shown
in Fig. 165, folded on itself, in such a way as to carry the
endoderm (en), into the centre, and thus form a thick- walled

THE DEVELOPMENT OF LAMELLIBRANCHS.

323

digestive cavity, with a small opening (g). This is the
gastrula stage, and a comparison with the sea-urchin will
show that it is essentially like the sea-urchin gastrula,
although it is not formed in precisely the same way. In
the sea-urchin segmentation is total and perfectly regular,
the segmentation cavity appears very early, and the endo-
derm cells are similar at first to the ectoderm cells, while
in lamellibranchs, segmentation, although total, is irregular,
the segmentation cavity does not appear until much later,
and the micromeres, which are to form the ectoderm, are,
from the first, quite different from the macromere, which is
to form the endoderm.

*•

FIG. 16o. Fl<t. 166. FIG. 167.

FIG. 165. —Embryo about thirty hours after fertilization, seen from
the side in optical section.

ec. Ectoderm, en. Endoderm. g. Orifice of invagination. sg. Seg-
mentation cavity.

FIG. 166. —Side view; and Fig. 167, Optical section of an embryo a
few hours older, in the gastrula stage.

ec. Ectoderm, en. Endoderm. ». Velum, g. Orifice of invagina-
tiou. a. Posterior dorsal angle of body.

In the sea-urchin the orifice of invagination becomes the
anus of the pluteus, but in the oyster it soon closes up,
and the anus is afterwards developed on the opposite side
of the body.

The edges of the orifice of invagination of the oyster
continue to approach each other, and finally meet and

324

HANDBOOK OF INVERTEBRATE ZOOLOGY.

unite, thus closing up the opening, as shown in Fig. 168,
and leaving the digestive tract without any communication
with the outside of the body, and entirely surrounded by
the outer layer. The embryos shown in Figs. 166 and 168,
are represented with the dorsal surface below, but in Fig.
169, and most of the following figures, the dorsal surface
is uppermost, for more ready comparison with the adult.
The furrow in which the orifice of invagination was placed
still persists, and soon a small, irregular plate (Fig.
168, s), makes its appearance at each end of it. These
little plates are the two valves of the shell, and in the
oyster they are separated from each other trom the first,
and make their appearance independently.

FIG. 168. FIG. 169.

FIG. 168. — A somewhat older embryo, in the same position as Fig.
166.

s. Shell. r>. Velum, a. Posterior dorsal angle of body.

FIG. 169. — A somewhat older embryo with the dorsal surface above.
m. Mouth, ec. Ectoderm, en. Endoderm.

Soon after they make their appearance, the embryos
cease to crowd to the surface of the water, and sink to
various depths, although they continue to swim actively in
all directions, and may still be found occasionally, close to
the surface. The region of the body which carries the
cilia now becomes sharply defined, as a circular projecting
pad, the velum (Fig. 168, f), and this is present, and is

THE DEVELOPMENT OF LAMELLIBRANCHS. 325

the organ of locomotion at a much later stage of develop-
ment. It is shown at the right side of Fig. 169.

The two shells grow rapidly, and soon become quite
regular in outline, as shown at s, in Figs. 169 and 172,
but for some time they are much smaller than the body,
which projects from between their edges around their
whole circumference, except along a short area, the area
of the hinge, upon the dorsal surface, where the two
valves are in contact.

The two shells continue to grow at their edges, and
soon become large enough to cover up and project a little
beyond the surface of the body, as shown in Fig. 172, and
at the same time muscular fibres make their appearance,
and are so arranged that they can draw the edge of the
body and the velum in between the edges of the shell. In
this way that surface of the body which lines the shell
becomes converted into the two lobes of the mantle, and
between them a mantle cavity is formed, into which the
velum can be drawn when the animal is at rest. While
these changes have been going on over the outer surface
of the body, other important in-
ternal modifications have taken
place. We left the digestive
tract at the stage shown in Fig.
1 68 , without any communication
with the exterior.

FIG. 170. — A still older embryo.
an. Anus. m. Mouth, s. Shell.

Soon the outer wall of the body becomes pushed in-
wards, to form the true mouth, at a point (Fig. 169, m),
which is upon the ventral surface, and almost directly
opposite the point where the orifice of invagination was

326

HANDBOOK OF INVERTEBI1ATE ZOOLOGY.

situated at an earlier stage. The digestive cavity now
becomes greatly enlarged, and cilia make their appearance
upon its Avails, the mouth becomes connected with the
chamber which is thus formed, and which becomes the
stomach, and minute particles of food are drawn in by
the cilia, and can now be seen inside the stomach, where
the vibration of the cilia keeps them in constant motion.
Up to this time the animal has developed without growing,
and at the stage shown in Fig. 168 it is scarcely larger
than the unfertilized egg, but it now begins to increase in
size. The oyster reaches the stage shown in Fig. 172 in

Fit;. 171.

FIG. 172.

FIG. 171. —A still older embryo.

an. Anus. a. Posterior dorsal an^le. ma. Mantle, v. Velum.
b. Body cavity, xt. Stomach, i. Intestine.

FIG. 172. — Vie\v of right side of an oyster embryo, six days old.
mu. Muscles. /.Liver, s. Shell. Other letters as in Fur. 171.

from twenty-four hours 1<> six days after the egg js ferti-
lized ; the rate of development being determined mainly
by the temperature of the water.

Soon after the mantle has become connected with the
stomach, this becomes united to the body wall at another

THE DEVELOPMENT OF LAMELLIBRANCHS. 327

point a little behind the mouth, and a second opening, the
anus (Fig. 171 and 172, an), is formed. The tract which
connects the anus with the stomach lengthens and forms
the intestine, and, soon after, the sides of the stomach
become folded off to form the two halves of the liver, as
shown in Fig. 172.

Various muscular fibres now make their appearance
within the body, and the animal assumes the form shown
in Fig. 172.

III. The Swimming Larva or Veliger.

It is difficult to rear the embryos, but the later stages
may be studied from specimens collected with the dip-net.
The swimming larvae or "Veligers" of marine lamellibranchs
are so abundant at the surface of the ocean during the
summer months that there is no difficulty in obtaining a
supply. In order to find them, allow the material which
has been collected with the dip-net or the tow-net (as de-
scribed in Section VII.), to stand over night in a jar of
sea-water. Then draw up with a dipping-tube a little of
the sediment which has settled at the bottom, and placing
it in a watch-crystal with a little sea-water, examine it
with a magnifying power of about fifty diameters. A little
j-c.-i rdiing will probably lend to the discovery of several
of the larvae lying upon the bottom among the sediment,
tightly shut up in their transparent, orbicular, or kidney-
shaped shells. The student will recognize them without
difficulty, since the sholl is shaped much like that of the
ndult. Having found a specimen, carefully note its posi-
tion with reference to adjacent masses of sediment, and
then try to rediscover it without a microscope. Having
done so, push the sediment away from it with a hair, and
sucking the specimen up into a dipping-tube, transfer it to
a small quantity of fresh sea-water. Place it under the

328

HANDBOOK OF INVERTEBRATE ZOOLOGY.

microscope, and allow it to remain undisturbed for ten or
fifteen minutes. The soft parts of a tightly-closed speci-
men are so crowded together inside the shell that it is dif-
ficult to study them, and almost as soon as a specimen is
fully expanded, it rises from the bottom and swims away
by the motion of the cilia of the velum, but a little pa-
tience will probably lead to the discovery of half-expanded
specimens, and these can be examined without much dif-

Fio. 173.

FIG. 173. — Right side of swimming larva, or Velic/er of Montacuta
ferruginosa, greatly magnified. (Copied with slight changes, from Love"n,
" Ent. dcr MolhiKca Acephala Lamellibranchiata," Fig. 104.)

D. Dorsal surface. V. Ventral surface. A. Anterior end. P. Poste-
rior end. o. Shell, a'. Hinge, aa. Anterior adductor muscle, b. Body
cavity, c. Ear. /. Flagellum. L Intestine. I. Liver. ?n. Mantle.
oe. (Esophagus, cv. Cilia of velum, v. Velum, vm. Retractor muscles
of velum.

ficulty. The larvse will probably belong to several species,
but most of those which are captured at the surface are
sufficiently like Fig. 173 for the student to make this figure
his guide in studying them.

THE DEVELOPMENT OF LAMELLIBRANCHS. 329

There is now a well-developed mantle chamber, into
which all the soft parts are retracted while the animal is at
rest. The velum (Fig. 173, v), is very large, and it fills
the ventral half of the anterior end of the cavity between
the shells, when retracted, but while the animal is swim-
ming, the velum is protruded from between the valves.
In most forms its outer surface is sunken, thus forming a
conical basin, with a fringe of locomotor cilia, (c, v), around
its rim. The depression in the centre allows the organ to
be folded together when withdrawn into the shell, but
when it is expanded, in swimming, it is nearly flat. In
most forms, a long flagellum (/*), arises from the bottom of
the depression, an(l projects beyond the cilia. There are
two large, flat muscles (v, m), on each side, to retract the
velum.

The mouth, being behind the velum, is in the posterior
half of the shell, and a long ciliated oesophagus (oe), runs
upwards and forwards through the liver (/), to the stom-
ach (s). A small tongue-like process from the posterior
wall of the oesophagus, runs out into its cavity, just below
the liver. The long, twisted intestine (z) , is freely movable
in the body cavity (6) , and the anus is near the mouth. In
most specimens, the auditory organs (e), can be seen a
little posterior to the oesophagus, and there are usually
two small pigmented eyes (not shown in the figure)
carried upon short, blunt tentacles, at the base of the
velum, anterior to the oesophagus.

The two renal organs, or organs of Bojanus, soon ap-
pear, as a pair of little tubular diverticula from the intes-
tine, near the anus, and at about the same time the ante-
rior adductor muscle («, a), and, soon after, the posterior
adductor, appears. The three pairs of ganglia appear
before the commissures between them. The velum, ten-

330

HANDBOOK OF INVERTEBRATE ZOOLOGY.

tades and eyes disappear; the foot grows out between
the mouth and anus, and the gills are developed as a row
of ciliated tentacles on each side of the body. With the
loss of the velum, the young animal usually settles to the
bottom, although there are certain forms which are able to
swim throughout life.

IV. The lawce of Anodonta. The eggs of Anodonta im-
plicata pass from the ovary into the gills during the latter
weeks of October, and they develop very rapidly. The
early stages are -much like those of the oyster, as far as
Fig. 169, except that the shell is not at first divided into
two valves, but is continuous across the middle line.
After this stage is reached, there is little resemblance
between the young Anodonta and a marine larva. The
shell and mantle develop very rapidly, while the digestive
organs become rudimentary, and are not developed until

five or six months later; in
Anodonta implicata, not. until
Do the next summer.

FIG. 174. — Anterior view of " Glo-
ehidium" larva of Anodonta, enclosed
in the egg-shell; magnified about one
hundred diameters. (Drawn from na-
ture by W. K. Brooks. )

b. Byssus. by. Byssus organ, e. Egg-
shell. A. Hooks. Is. Left valve of shell.
m. Posterior adductor muscle. /•*. Hi^ht.
valve of shell, s. Setae, e. Velum.

If a female Anodonta be examined at any time between
November 1st and April 1st the outer gills will be found
distended by a brownish-red mass, which microscopic ex-
amination shows to be made up of the embryos, still en-
closed in the egg-shells. One of them is shown from in
front in Fig. 174, and in ventral view, after the removal

THE DEVELOPMENT OF LAMELLIBRANCHS,

331

of the egg-shell, in Fig. 175. The two valves of the shell
are united by a hinge, and they are somewhat triangular
in side view. The elasticity of the hinge ligament is so
great that it may open the valves
until they lie in the same plane.
The ventral angle of each valve
is bent inwards to form a mova-
ble toothed hook (Figs. 174 and
175, A), from which the larva
has received its name " Glochi-
dium."

FIG. 175. — Ventral view of the same
larva, with the valves of the shell opened.
(Drawn from nature by W. K. Brooks.)

Letters as in Fig. 174.

The valves are lined by the large spherical cells of the
mantle, and from some of them large stout setae (s) pro-
ject into the mantle cavity. The valves are closed by a
very large and well-developed adductor muscle (m) ; but
the elasticity of the hinge ligament is so great that re-
peated efforts are necessary before the animal can close the
shell completely after it has been thrown open. The space
between the halves of the mantle is usually almost entirely
filled by a long, clastic, tough, brown, coiled thread, the
/jy.w.s', which is shown at b. The byssus is formed in a
long, tubular byssus organ (bg) which is coiled inside the
left valve of the shell, between it and the cells of the
mantle. The Glochidium has no ears or eyes, no gills
and there is no projecting locomotor velum, although
a row of cilia (?»), at the anterior end of the body,
may be a rudimentary velum. The digestive cavity
is not divided into regions, but is a simple pouch with

332 HANDBOOK OF INVERTEBRATE ZOOLOGY.

thick walls and a single large opening, just under the
letter v of Fig. 174. The embryo of Anodonta reaches
this stage of development within a few days after the eggs
are laid, and it remains almost without change until late
in the following spring. The parent then discharges the
larva? through the cloacal siphon into the water, where
they float for a short time. It is probable that all that
settle to the bottom die. Others are entangled by their
byssus threads to the tails, dorsal fins and gills of small
fishes. These close the valves of the shell onto the body
of the fish, driving the hooks into it. The setae probably
excite inflammation in the skin of the fish. At any rate the
epithelial cells of the skin grow at an unnatural rate, and
soon build up a covering over the larva, which is thus
enclosed in a brood-pouch, where it completes its develop-
ment, acquires gills, an oesophagus, stomach, intestine,
and renal organs and heart, and then escapes from the
brood-pouch and falls to the bottom to complete its
growth.

XXIX.— THE GENERAL ANATOMY OF THE SQUID.

(Lpligo Pealii. )

WITH a little thought the student should be able to
trace out the general anatomy of any Dibranchiate (Vphal-
opod by the use of the following description, but as the
various forms differ greatly, he should, if possible, study
one of the squids. The description has been written from
Loligo Pealii, but any species of Loligo or ( hnmastrephes
will answer for laboratory work.

Specimens may be obtained by the dredge or trawl, but
as they are frequently captured in great numbers by fish-

GENERAL ANATOMY OF THE SQUID.

333

ermen, in their nets, the best way to obtain a supply is
by a visit to some fishing station upon the seashore.

If they are to be preserved in alcohol for dissection,
they should be placed in about fifty per cent alcohol for
a few hours, before they are transferred to strong alcohol,
and the latter should be changed once or twice during the
first three or four days.

I. External Form.

1 . In an alcoholic or a fresh specimen notice : (a) the
long cylindrical body ; (b) the somewhat movable head,
with its large eyes (Fig. 176, d), and with five pairs of
tentacle-like arms (Fig. 176, «', a", a'", a"", b) ; (c) the
mouth situated in the centre of the space between the
bases of the arms ; (c?) the tip of the brown, horny beak,
which usually protrudes a little from the mouth ; (e) the
pair of large triangular fins, which
are joined to the surface of that
third of the body which is farthest
from the head ; (/") a crenated fold
of membrane, the olfactory organ
(Fig. 176,/), on each side of the
head, behind the eyes.

FIG. 176. — Side view of the head of
Loligo Pealii. (Drawn from nature by
W. K. Brooks.)

o. Dorsal arm. rtiv. Ventral arm; the
tip of this arm on the left side becomes
modified in the male as the hectocotylus).
6. Grasping arm. c. External opening of
eye. d. Eye. /. Olfactory organ. <j. Siphon
curtilage, h. Neck cartilage. L Lateral
chamber of siphon, e. Ventral chamber of
siphon. k. Retractor muscle of siphon.
I. Retractor muscle of head.

FIG. 176.

334 HANDBOOK OF INVERTEBRATE ZOOLOGY.

For convenience in description we shall in the present
paper speak of the end of the body, where the head is
placed, as anterior, and the opposite pointed end as pos-
terior; the surface to which the fins arc attached we shall
call dorsal, and the opposite surface ventral. The student
must not infer, however, that these terms are of morpho-
logical value, or that the regions which they designate in
the Squid are the same as the regions designated by sim-
ilar terms in other Molluscs.

2. Place the animal with its dorsal surface uppermost,
and notice : —

«. The long cylindrical body, ending posteriorly in the
pointed, arrowhead-shaped Hn.

b. The small dark-brown pigment spots, or chromato-
phores, which cover the surface of the body and head.
Examine the chromatophores upon various parts of the
bod}7 with a lens. In an alcoholic specimen most of them
are flat", brown, oval, plate-like bodies, but some may be
found in which the outline is irregular, and with radiating
processes running out into the surrounding tissues. In a
living animal the chromatophores are brightly colored,
and are constantly undergoing changes of shape and >i/e,
expanding until the edges of adjacent ones almost come
into contact, and then contracting to almost invisible spots.
Owing to these changes, blushes of color are continually
flashing over the surface of the body, and then suddenly
disappearing.

The structure and changes of the chromatophore can be
best studied in the small transparent embryos, which are
frequently to be found at the surface of the ocean during
the summer month-.

c. Anteriorly the body proper ends in a free edge or
collar, the margin of the mantle, which is separated from
the head by an interspace, the mantle <•//<>/, /her.

GENERAL ANATOMY OF THE SQUID. 335

On the median dorsal line the mantle gives rise to a
short flap, which projects forwards over the head.

d. Turn this flap over and slit the thin integument of
its inner surface, and notice inside it the anterior end of
the dark-brown, horny, internal shell, or pen.

e. Make an incision through the integument, along the
median dorsal line, from the base of this flap to the pos-
terior end of the body. Turn back the integument on
each side of this incision, and notice the internal shell in
its capsule.

( 1 . ) Raise up one end of the shell and pull it out of the
capsule, noticing that it is not attached to the walls in any
way, but is entirely free.

(2.) The shell is thin, transparent, and horny, and con-
sists (a) of a central shaft, which runs from end to end,
like the quill of a feather, and which is strengthened by
three parallel ridges, and (6) of two lateral portions, like
the vanes of a feather, one on each side of the posterior
live-sixths of the shaft, and strengthened by a marginal
ridge.

(3.) Make a sketch of the shell.

(4.) Notice that the capsule of the shell is a closed sac,
lined by a delicate membrane, and without communica-
tion either with the exterior or with the body cavity.

f. In a dorsal view of the head, notice the protruding
eyes, and three pairs of arms (Fig. 176, a, a', a"), which
are visible in a dorsal view. Notice that these arms are
symmetrically arranged with reference to the dorsal me-
dian line.

g. Make a sketch of the dorsal view of the animal.
3 . In a ventral view notice : —

a. The delicate parallel bands of muscles which extend
from the body to the lateral edges of the fin.

336

HANDBOOK OF INVERTEBRATE ZOOLOGY.

b. Two tooth-like prolongations of the anterior edge
of the mantle, behind the eyes.

c. The end of the siphon (Figs. 176, e, 177, d),

projecting from the mantle
chaniber; on the median
ventral line, bending to-
wards the ventral surface,
and ending in a transverse
oval aperture (Fig. 177, c),
which is furnished with a
valvular fold.

d. In the ventral view of
the head notice a pair of arms
(Fig. 177, aiv), one on cadi
side of the median line.

FIG. 177. — Male specimen of
Loligo Pealii, with the mantle
opened to show the body and
gills. (Drawn from nature by
W. K. Brooks.)

a. Head. oiv. Ventral arm.
av. Grasping arm. b. Eye. c. Si-
phon, d. Cartilages of siphon.
e. Cartilages of mantle. /. Free
edge of mantle, f/. Mantle, ft. Gills.
i. Rectum, k. Retractor muscles of
siphon. JH. Ink bag. n. Penis.
q. Intestine. r. Branchial veins,
s. Gill muscles, t. Branchial ar-
tery, u. Branchial heart. <>. K'enal
organs, p. Orifice of renal organ.
v. Mantle artery, w. Posterior veine
cavae. x. Visceral sac. y. Mantle
cavity.

Kit;. 177.

e. Outside the bases of these arms a pair of much
longer ones, the grasping arms (Fig. 177, av), each of

GENERAL ANATOMY OF THE SQUID. 337

which consists of a long, sleuder, cylindrical' shaft, termi-
nating in a large rhomboidal expansion, upon which are
four rows of cup-shaped suckers or acetabula, while the
remaining eight arms have two rows each of acetabula.

/. Make a sketch of the ventral surface.

g. Examine the acetabula with a hand lens ; notice : —

(1.) The short peduncle or stem.

(2.) The enlarged terminal cup, on the outer or flat
surface of which notice : —

(a.) The membraneous marginal lip, which encircles the
aperture.

(/;.) Inside this a horny ring, with its outer or exposed
edge serrated with fine teeth.

(c.) Within this a shallow cavity, at the bottom of
which is a flat surface, the piston.

(V.) Cut a longitudinal section of one of the acetabula,
and with a hand lens notice that the piston is made up of
a mass of muscles, which are attached to the bottom of
the cup, and so arranged as to pull back the piston, by
which the sucking action of the acetabula is affected.

II. The Mantle Chamber.

Xotice that while the anterior edge of the mantle is not
attached to the head at any part of its circumference, it is
in contact with it at three nearly equidistant points, on
the median dorsal line and at the sides. Open the mantle
cavity by an incision through the integument, from the
anterior margin nearly to the posterior end, and a little to
the left of the median line. Place the animal under
water, and turn back the halves of the mantle, in order to
expose its cavity. Xotice that while the mantle cavity
extends upon the sides and ventral surface, nearly to the
posterior end of the body, it is quite shallow on the me-
dian dorsaj line, and about an inch from its anterior mar-
gin the mantle is joined to the neck.

338 HANDBOOK OF INVERTEBRATE ZOOLOGY.

a. On the dorsal surface of the neck notice the dorsal
mantle cartilage (Figs. 170, h, 1(JO, /), an elongated, flat-
tened, cartilaginous plate, with a groove along the middle
of its surface, and a ridge on each side of the groove.

b. Lying upon this plate, but covered by the integu-
ment of the mantle, notice the upper end of the pen
(Fig. 190, w)» with a longitudinal ridge which fits into the
groove in the plate.

c. On each side of the body the edge of the mantle is
produced forwards, forming a tooth-shaped point.

d. On the inner surface of the mantle, in the same
region, is a longitudinal ridge (Figs. 177, e, 190, z),
about an inch long.

e. On the outer edges of the base of the siphon are
two x!])]u>ii(rt curtildijf* (Figs. 176, g, 177, d, 190, //),
each of which carries a longitudinal groove, into which
the ridge on the inner face of the mantle fits.

f. The head is attached to the mantle by a neck, which
is mainly composed of four large muscles, the two dorsal
retractors of the head (Fig. 176, ?), and the two ventral
retractors of the siphon (Fig. 176, A').

g. On each side of the first pair of muscles, just poste-
rior to the dorsal mantle cartilage, notice a pair of nerves
which pass out from the neck into the mantle, and end in
the large r/anylia stellata, which supply the mantle with
nerves.

//. The siphon is now seen to be somewhat pyramidal
in shape, and wrapped avound the neck, with the small
end pointing forwards ; its cavity is divided into three
chambers.

1. The funnel-shaped ventral chamber (Fig. 176, e),
communicating with the mantle cavity at its broad end,
and with the small valvular external aperture at the small
end.

GENERAL ANATOMY OF THE SQUID. 339

2. On each side of it is a lateral chamber (Fig. 176, i),
open posteriorly but closed anteriorly, and entirely sepa-
rated from the cavity of the ventral division.

It will be seen that when the walls of the mantle cham-
ber contract to expel the contained water, any water which
is driven into these lateral chambers will simply force their
free posterior margins out against the mantle, thus forming
a valve to prevent the water from passing out.

The only exit will then be through the ventral chamber ;
and during life, the stream of water which is thus driven
through the ventral siphon at each respiration, is the prin-
cipal means of locomotion.

The superficial appearance of the contents of the mantle
chamber varies considerably, according to the sex of the
specimen. When the mantle of a male specimen is laid
open it presents the appearance shown in Fig. 177, but
most of the structures shown in this figure are, in the
female, covered up by the large, hemispherical, white, finely
striated nidamental yhoitlx. When these are removed the
parts under them are much like those of the male, but the
student should, if possible, select a male specimen for
studying the general anatomy.

i. In the male specimen, notice, in the middle line, just
behind the siphon, the rectum (Fig. 177, q), which is
bound down onto the- other viscera by a mesenteric fold.
At its anterior end notice the anus (/), guarded by a pair
of ear-like valves. Dorsal to the intestine, but projecting
beyond it so as to be visible on each side of it in a ventral
view, notice the ink bag (Fig. 177, m).

j. Running forward from it on the inner surface of the
intestine, notice the ink duct, which opens into the siphon,
behind the tip of the rectum.

k. In the male, notice on the right side of the intestine

340 HANDBOOK OF INVERTEBRATE ZOOLOGY.

the external opening of the reproductive organ, situated
at the end of . an elongated papilla (Fig. 177, n).

I. On each side of the intestine, about an inch behind
the anus, a small papilla, the opening of the renal organ
(Fig. 177, X).

m. Posterior to these orifices are the renal organs, a

O 7

pair of transparent-walled pouches (Fig. 177, o), with an
indefinitely marked outline, one on each side of the rec-
tum ; near the anterior ends of these organs, notice that
the rectum bends downwards, and passes behind them.

n. Running out from behind each renal organ into the
surface of the mantle is the branchial vein (Fig. 177, ?*),
through which aerated blood is returned from the gills "to
the heart.

0. On each side of the body is a plumose gill (Fig.
177, /*), which is free ventrally, but attached dorsally to
the mantle. Notice that the branchial vein runs along its
free ventral surface.

p. Just behind the point where the branchial vein
j lasses below the renal organ, notice on each side of the
body a small white oval body, the branchial heart (Fig.
177, u), covered by a delicate transparent pericardium.

1. Notice the branchial artery (Fig. 177, ?), which
passes from each branchial heart to the gill, and runs
along the line upon which the dorsal surface of the gill is
joined to the mantle.

q. On the median line, a little posterior to the branchial
hearts, a large artery, the median mantle artery (Fig.
177, v), runs from the surface of the mantle chamber to
the inner surface of the mantle, where it « divides into an
anterior and a posterior branch.

r. On each side of the point where this artery leave-
the body, a large cone-shaped organ may usually be

GENERAL ANATOMY OF THE SQUID. 341

found, running backwards and downwards around the
body into the mantle, where it divides into an anterior
and a posterior branch, which pass into the muscular layer
of the mantle. These bodies (Fig. 177, w) are made up
of an artery and a vein, united in a common fold of me-
sentery, the lateral mantle artery and the posterior vena
cava. In an alcoholic specimen the vein is usually greatly
distended by coagulated blood.

s. Posterior to these arteries is the large visceral sac
(Fig. 177, #), reaching to the posterior end of the body,
and covered by a delicate, transparent mesenteric mem-
brane, which is reflected out along the ventral mantle
artery and along the back, into the inner face of the
mantle.

t. Make a drawing, showing as many of these parts as
possible.

III. The Circulatory and Renal Organs.

With a pair of fine-pointed scissors cut through the thin
membrane of the two renal organs, by a transverse incision
just behind their external openings ; and placing the speci-
men under water, pull off, with a fine pair of forceps, the
wall of the renal organs, thus exposing their cavities
(Fig. 178, g). With a stream of water, or a fine brush,
gently wash away the fine white granular substance, which,
in an alcoholic specimen, usually fills the cavity, and notice
the intestine (Fig. 178, /*), which lies between the two
chambers.

a. On each side of this, notice a large, white, glandular
body, which almost entirely fills the cavity of the renal
organ ; this is the glandular portion of the anterior vena,
cava (Fig. 178, i).

The anterior ends of the vena? cavse of the two sides of
the body bend down under the intestine, where they unite
to form one median trunk, which will be noticed later.

342

HANDBOOK OF INVERTEBRATE ZOOLOGY.

Their posterior ends are flattened, and lie near the sur-
face of the body. Notice that the cavity of the renal organ

entirely surrounds the
glandular portion of the
blood-vessel.

FIG. 178. — Superficial dis-
section of the ivnal and cir-
culatory on,r;iHM>l' male speci-
men of Loligo Pealil. ( I )rawn
from nature by W.K. Brooks. )
The capsules of the renal
organs are opened, and the
blood-vessels an- freed from
the adjacent organs.

a. Rectum, cut across.
It. Gills, o. Branchial veins.
(7. Ink bag. e. Penis. /. Open-
ings of renal organs. <j. < 'av-
ity of renal organ. A. Intes-
tine. L Glandular portion of
anterior vena cava. /,-. Sy—
teniic, heart. /. Branchial ar-
tery. w. Gill muscle. n. Nu-
trient artery of gill. o. Bran-
chial heart. j>. Glandular
portion of posterior vena
cava. </. Enlarged portion
of posterior vena ca\ a. r. Lat-
eral mantle artery. .«.-. Stom-
ach. t. (Esophageal end of
stomach. ». Reproductive
organs. s'. Blind sac of
stomach. ('•. Capsule of ab-
dominal viscera, or perito-
neum. .r. Artery to stomach
and mantle.

FIG. ITS.

b. The anterior vena cava runs backwards as far as the
branchial heart, where it unites with a much shorter
glandular structure, the glandular portion of the posterior

GENERAL ANATOMY OF THE SQUID. 343

vena cava (Fig. 178,^?), which is flattened, and nearly as
wide as long.

c. Notice that the cavity of the renal organ (Fig.
178, #), extends backward only as far as the posterior
end of this structure.

d. Following the posterior vena cava backwards, it will
be found to be a thin-walled tube (Fig. 178, q), capable
of great distension, and usually filled with coagulated
blood. It runs back around the body into the mantle.

e. Carefully dissect^ away the membrane which covers
it, and notice close beside it the dorsal mantle artery
(Fig. 178, r).

/. Opposite and outside of the point where the anterior
and posterior venae cavse meet, notice the branchial heart
(Fig. 178, o), in a separate pericardial chamber.

g. Open this chamber and turn the heart over, and
notice that the two vense cavae open into it, and that a
large vessel, the branchial artery (Fig. 178, Z), passes
from it to the gill (5).

Trace this vessel out along the line where the gill is
joined to the mantle, and notice that it gives rise, at right
angles, to a series of small vessels, which pass into the
gill leaflets, and there give rise, to still smaller branches.

h. Dissect away the connective tissue which binds the
ink bag and rectum to the surface of the body, until these
organs can be turned to one side, as shown in Fig. 179,
at d and 7^, to expose the structures below them.

1. Notice that the anterior vena cava of the left side
gives off a small glandular branch to the intestine.

2. The two vense cavse (Fig. 179, i, z), then pass below
the intestine, and unite to form a large flat glandular body,
which lies upon the median line, and is contained in a pro-
longation of the renal organs.

344

HANDBOOK OF INVERTEBRATE ZOOLOGY.

3. In the centre of this body the single, non-glandular,
transparent, thin-walled anterior vena cava (Fig. 179, 10),
arises, and runs forward on the median line, through the

siphon to the head.

FIG. 179. — Deeper dis-
section of the circulatory
organs of a male speci-
men of Loligo Pealii.
(Drawn from nature by
W. K. Brooks. ) The pos-
terior venae cavse (7, q)
have been cut. and the
right anterior vena cava
has been turned to one
side to show the systemic
heart. The renal organs
have been removed, and
the intestine (//) and the
ink bag (d) turned to the
right, to expose the ante-
rior vena cava, theliver(S),
and the spleen (12).

The reference letters are
the same as in Fig. 178.

I. Head. 2'. Siphon.
S. Valve in orifice of si-
phon. 4- Si phonal carti-
lage. 5. Lateral chamber
of siphon. 6. Median
chamber of siphon. 7. Re-
tractor muscle of head.
8. Retractor muscle of
siphon. '9. Liver. 10. An-
terior median vena cava.

II. Hepatic ducts.
12. Spleen. 13. Anterior
aorta. 14. Posterior
aorta.

Fio. 179.

4. Near the siphon it gives rise to a branch which pa
towards the dorsal surface, and penetrates the soft white
//'•'-/• (Fig. 179, 9), which lies between the large retractor
muscles (Fig. 179, 7, 8,) of the head and siphon.

GENERAL ANATOMY OF THE SQUID. 345

5. Lift up the glandular vena cava of one side, and
notice, near the point where it unites with its fellow, a
glandular branch, which runs downwards into the sub-
stance of a white glandular body, the spleen? (Fig. 179,
12), which lies below it.

i. The systemic heart and arteries.

Remove the branchial heart and venae cavse from the left
side of the body, and notice below them, on the median
line of the body, the smooth, white systemic heart (Figs.
178, k, 179, &), running obliquely across the body, with
its anterior end to the left.

1. Near the middle of its posterior margin, the posterior
aorta (Fig. 179, 14), originates, and passes backwards on
the median line.

2. This soon divides into three mantle arteries, already
noticed (v, v, v).

3. Notice the branchial vein (Fig. 179, c, c'), which
brings back the blood from the left gill, and opens upon
the centre of the rounded left side of the systemic heart.

4. The right branchial vein opens into the pointed right
side of the heart.

5. On the left side of the body, the anterior end of the
heart gives rise to the anterior aorta (Fig. 179, 13), which
runs forwards to the left of and below the spleen. Its
subsequent course will be traced in connection with the
digestive organs.

IV. The Digestive Organs.

Remove both veme cavse ; cut the anterior aorta, and
remove the systemic heart, and carefully strip oif the del-
icate membrane which covers the visceral mass.

(t. The greater part of this mass is formed by a thin,
delicate-walled pouch, the blind sac of the stomach
(Figs. 178, »', 180 and 181, k).

346

HANDBOOK OF INVERTEBRATE ZOOLOGY.

?>. At its anterior end this opens into the much smaller,
muscular, thick-walled stomach (Fi<rs. 17s, *, 180 and
181, /*, i).

c. At the anterior left corner of the stomach are the

as8ophagus (l-'i^s. 1. so and
181, c), and intestine
(Figs. 180 and 181, n),
side by side.

d. The intestine bends
upwards between the two
p halves of the spleen (Figs.
180 and l.si, </), and soon
becomes constricted to
form the rectum (Fig.
181, o).

FIG. 180. — Ventral view of
the digestive organs of Loligo
Pealii. (Drawn from nature by
W. K. Brooks.)

Reference letters for Figs.
ISO ami 181: —

a. Nerves miming to ganglia
stellata. b. Liver, c. (Esopha-
gus, d. Anterior aorta, e. Point
where (esophagus and aorta pass
out of liver on dorsal surface.
/. Hepatic ducts. .'/. Spleen.
A. CEsophageal chamber of stom-
ach, i. Left side of stomach.
k. Blind sac of stomach. I. Ar-
tery to testis. m. Testis. n. In-
testine, o. Rectum, p. Anus.
q. Ink bag. r. Ink duct. s. An-
terior aorta, t. .Systemic lu-art.
». Branchial veins. r. Poste-
rior aorta.

PIG. 180.

GENERAL ANATOMY OF THE SQUID.

347

e. The oesophagus may be traced forwards on the left
side of the body to a point just in front of the spleen,
where it enters the liver (Figs. 180 and 181, 6).

f. The anterior
aorta (Fig. 180, s),
will be seen to follow
the same course, and
to pass into the liver.

g. Carefull}' raise
up the liver (Figs.
180 and 181, b), and
notice that the oeso-
phagus (Fig. 181, c)
and aorta (Fig. 181, c?)
pass entirely through
it, and run forwards
on its lower surface
to the head.

h. On the dorsal
surface of the anterior
end of the liver are a
pair of small, com-
pact, white glands,
the posterior salii'm-i/
glands, in contact with
each other on the mid-
dle line. Their ducts
pass into the head
alongside the (esopha-
gus, and they will be
noticed in the descrip-
tion of the head. Fl0' 181' — Oorsal view °f tne digestive
organs of Loligo Pealii. (Drawn from na-
liunnmg out from turn by W. K. Brooks.)
under them, not; e For explanation of letters see Fig. 180.

348 HANDBOOK OF INVERTEBRATE ZOOLOGY.

the nerves (Fig. 181, a, a), which pass to the ganglia
stellatu.

i. On each side of the esophagus, where it passes into
the ventral surface of the liver, is a delicate, transparent,
hepatic duct (Fig. ISO,/"), which may be traced into the
spleen (</), and through this organ to the stomach.

j. Raise up the stomach, and notice below it, in a cap-
sule of its own, the testis or ovary, according to the sex
of the specimen. A large, compact, white body on the
median line, and on the left of it notice the accessory
reproductive organs.

V. Divide the head vertically, with a razor, by a single
cut through it, along the median line. In the section thus
made notice :

a. The opening of the mouth, between the bases of the
arms.

b. The two horny jaws, one on the dorsal side of the
mouth, and one on the ventral side. The former (Fig.
185,/'), is smaller than the ventral one, cZ, into which it
shuts.

c. The nearly spherical, muscular, buccal body.

1. The cavity of the oesophagus (Fig. 185, c), running
through it, near its dorsal surface.

2. The lingual ribbon (Fig. 185, &), lying upon the
floor of the oesophagus.

d. Behind the buccal body the small oesophagus, (c),
runs backwards through the head and neck to the bod}',
where it lies dorsal to the liver, as already noticed.

e. In the section notice the cartilaginous ring or cranium
which surrounds the oesophagus, in the posterior portion
of the head.

f. The ganglia of the nervous system, which are ar-
ranged in a ring around the oesophagus, within and ante-
rior to the cranium.

GENERAL ANATOMY OF THE SQUID. 349

VI. The Reproductive Organs of the Male.

a. Carefully examine the tip of the left ventral arm of
a male specimen, — the arm which is marked alv in Fig.
177, and notice that the acetabula are absent, and that
their stalks become modified into elongated papillae, which
are different in shape from the stalks of the acetabula on
the other arms. Examine the tip of the corresponding
arm of a female, and notice that it is not different from
the tips of the other arms.

The portion of the left ventral arm of the male, which
carries the papillae, is a rudimentary hectocotylus, or copu-
lating organ. It does not seem to be a reproductive organ
in the squid, although it is fully developed and functional
in many other Cephalopods.

b. The Testis. This is a somewhat flattened, pear-
shaped gland (Figs. 180 and 181, m), which lies near the
posterior end of the visceral mass, on its dorsal surface.
It is enclosed in a thin, transparent, membraneous capsule,
and the blind sac of the stomach is on its right side and
ventral surface. Its upper surface is irregularly rounded ;
its lower end pointed ; its ventral surface flattened and
slightly concave, and its dorsal surface is convex, and
marked by three or four parallel longitudinal ridges,
which fit the longitudinal folds of the pen. Notice the
genital artery (Fig. 181, I), which enters the testis on its
upper edge, and helps to support it in its capsule. Notice
also that a delicate membrane forms a sort of mesentery,
which binds the testis to the dorsal wall of its capsule.

c. No duct is joined to the testis directly, and the ripe
spermatozoa escape from the seminiferous tubules which
open near the middle of the ventral surface, and pass into
the cavity of the capsule, from which they pass into the
excretory duct.

350

HANDBOOK OF INVERTEBRATE ZOOLOGY.

This is a complicated mass of twisted and convoluted
tubes, which is bound together, by connective tissue, into
a compact body, which lies on the left of the testis. Its
a posterior end (Fig. 182, h) does not

Vii join the testis, but opens into its
Ml capsule, from which it receives the
spermatozoa after they have escaped
from the testis.

In order to examine the excretory
duct, carefully separate the various
folds, by dissecting away, under
water, the connective tissue which
binds them together. It will then
be found to be divided into four
regions, the ras deferens, the vesi-
cit/f/ xnitt'itd/t'x, the prostate yluml ,
and the spermatophoric receptacle.

FIG. 182. — Male efferent duct of Loligo
vulgaris. From Brock, " Gescfilechtsorr/ane
</'/• Cephalopoden." Z.Z. xxxii., l, Taf. 1,
Fig. 3.)

a. Penis. 6. Spermatophore sac. c. Vas
efferens. d. Blind sac of vas efferens..
e. Prostate. /. Vesicula seminales. g. Vas
deferens. h. End of vas deferens which
opens into capsule of testis.

1. The vas deferens (Fig. 182, ^), is a small, much con-
voluted tube, which opens, at its posterior end, into the
left side of the capsule of the testis. Its distal end
passes abruptly into the second region.

2. The vesicula seminalis (Fig. 182, jf), is a much larger
tube, which again may be divided into a proximal convo-
luted portion and an unfolded distal portion.

GENERAL ANATOMY OF THE SQUID.

351

3. The third division, or vas efferens (Fig. 182, c), is a
long, straight, thin-walled tube, which passes backwards
to open into the posterior end of the fourth division.

4. This is the sper-
matophoric receptacle.
It is much larger and
longer than any of the
other regions, and it
may again be divided
into a distal portion
or pen is (Figs. 182, a,
177, », 178, c, 179, e),
with thick, muscular
walls, and an enlarged
proximal portion or
spermatophoric pouch
(Fig. 182, b), with
thin transparent walls,
inside which the long
white thread-like sper-
matophpres may usu-
ally be seen.

FIG. 183. — Female re-
productive organs of Loligo
vulguris. (From Brock,
Taf. 11, Fig. 20.) Drawn
by S. Garman.

a. Mantle. 6. Gills.
c. Siphon. d. Ink bag.
e. Blind sac of stomach,
turned to one side. y. Gland
of oviduct, h. Terminal por-
tion of oviduct, od. Folded
transparent portion of ovi-
duct, o. Ovary. FIG. 183.

352

HANDBOOK OF INVERTEBRATE ZOOLOGY.

5. A small, compact, accessory gland, the prostate (Fig.

182, e,) opens into the vas efferens close to its proximal

end, and near this is a blind pouch (d).

d. The spermatophores. The spermatophore of Loligo

Pealii (Fig. 184) is a white, slender rod or thread, about
half an inch long. When magnified
it is seen to consist of three parts :
an outer tubular sheath (a] : a packet
of spermatozoa (b), which fills nearly
two-thirds of the sheath ; and a long,
complicated, discharging body (c),
which is coiled up so as to form a
long, elastic spiral spring.

FIG. 184. — Spermatophore of Loligo
Pealii, magnified about thirty diameters.
(Drawn by W. K. Brooks from a sketch
from nature by H. J. Rice.)

a. Sheath or capsule. 6. Packet of sper-
matozoa, c. Discharging body. d. A single
FIG. 184. spermatozoon more magnified.

When a fresh spermatophore is placed in water, the
sheath becomes ruptured at the end (d), and the dis-
charging body springs out, dragging the packet of sper-
matozoa after it.

VII. The Reproductive Organs of the Female.

These are the ovary, the oviduct, the gland of the ovi-
duct, the nidamental glands, and the accessory nidamental
glands.

a. The nidamental glands. When the mantle of a female
specimen is laid open, the region of the heart and renal
organs will be found to be covered by a pair of large,
white, rounded, laminated bodies, the nidamental glands,

GENERAL ANATOMY OF THE SQUID. 353

which open at their anterior end into the mantle cavity.
They excrete the capsules of the egg masses. In front
of them, wrapped around the intestine and ink bag, are
the much smaller accessory glands.

b. The ovary (Fig. 183, o) is situated, like the testes, in
the dorsal portion of the posterior end of the visceral
mass, and it is enclosed, like the testes, in a capsule, into
which the eggs escape, to be taken up by the oviduct.
The oviduct (Fig. 183, o, d) is a long, transparent, foli-
ated tube, opening into the left side of the capsule of the
ovary.

c. Near its anterior end the walls become thickened to
form the gland of the oviduct (Fig. 183, </), and in front
of this the oviduct runs forwards as a thick- walled tube
(Fig. 183, h), which opens into the mantle cavity on the
left side, near the base of the siphon.

VIII. The anatomy of the brain, the sense organs, and
the buccal body, can be best studied in a series of trans-
verse sections through the head, and very small specimens
should, if possible, be selected, as the sections may then
be made thin enough for microscopic examination.

During the summer, small squids, from half an inch to
an inch and a half long, may frequently be found swim-
ming at the surface of the ocean during the middle of the
day, and they may be captured with a hand-net. They
should be placed for three hours in a one-tenth per cent
solution of chromic acid. They should then be placed
for about six hours in a three-tenths per cent solution,
and then, for the same time, in a one per cent solution.
They may then be placed in seventy per cent alcohol,
which should be changed in about twenty-four hours for
eighty per cent. After they have been in this for about a
day, they may be kept in eighty-five per cent or ninety

354

HANDBOOK OF INVERTEBRATE ZOOLOGY.

per cent alcohol until they are wanted. They should
then be placed in absolute alcohol for ten or twelve hours,
after which they may be mounted in paraffine, as described
in Section VII. A series of thin sections through the
head should then be made and mounted in balsam for
microscopic examination.

«. In a section through the anterior end of the head,
notice : —

1. The cut surfaces of the five pairs of arms (Fig.
18fi, a, a, a, a, a}.

2. Near the centre of each arm a brachial ganglia (Fig.
186, 6, b, b, 5, 6), which consists of a central axis of
white matter or nerve fibres, surrounded by a layer of
gray matter or ganglion cells, outside of which the g:m-

glion is covered by an investing
sheath.

FH;. !$.">. — Diagram of vertical sec-
tion of huccal body. (Drawn from na-
ture by W. K. Brooks. )

n-'i. The plane of the section shown
in Fl'j;. ISC,.' ,—<l. The plane of the sec-
tion shown in Fie;. 187. c. (Esophagus.
d. Superior or ventral mandible, e. In-
ferior or dorsal mandible. /. Muscles
of dorsal mandible. ft. Muscles of
ventral mandible. L Tongue, k. Ra-
dula.

FIG. 185.

3. In some of the sections, the transverse or circular
commissure, which connects these ganglia with each other,
will be found. Notice that the fibres of the commissure
pass through the layer of gray matter into the central axis
of white matter of .the ganglia.

4. In the centre of the section notice a large oval body,
the transverse section of the buccal mass.

GENERAL ANATOMY OF THE SQUID. 355

5. On the ventral edge of this is a space (Fig. 186, c),
the mouth.

6. Dorsal to the mouth is the section of the small dorsal
jaw (d) of the beak, which is shown in longitudinal section
at (d), in Fig. 185.

FIG. 186.

Fro. 186. — Transverse section through the anterior end of the head of
a young specimen of Loligo Pealii ; magnified about twenty diameters.
(Drawn from nature by W. K. Brooks.) The shading in fine lines shows
the course of the muscular fibres.

a, a. a. a, a. Transverse section of the arms. 6, b, b, b, b. The bra-
chial ganglia and commissures. c. Pharynx, d. Dorsal mandible.
e. Ventral mandible. /. Muscles of dorsal mandible, g. Muscles of
ventral mandible, h. Lip. i. Tongue.

7. Between the lateral portions of this jaw the muscle (f)
which moves it.

8. The sides of the buccal mass are formed by the two
large muscles (</) which move the ventral or larger man-
dible.

356

HANDBOOK OF INVERTEBRATE ZOOLOGY.

9. This mandible is shown in section at e, in the ventral
margin of the mouth.

10. A rounded body, the tongue (0, projects into the
cavity of the mouth on its ventral side.

b. In a section near the middle of the bucral body (Fig.
187), notice : —

1. The commissures (6, 6), which run down into the head
from each of the bnu-hiul ganglia. At first these com-
missures lie in the axes of the arms, but in a section a
little farther from the anterior end they will be found to
be in the space around the buccal body.

FIG. is;.

FIG. 187. — Section a little further back, less highly magnified.
(Drawn from nature by W. K. Brooks.)
A:. Kadula. Other letters as in Fig. 186.

2. The buccal body is, at this level, almost entirely made
up of the large mandibular muscles (Fig. 187, g).

3. In the central axis, but nearer to the dorsal than to
the ventral surface, notice the pharynx (c).

4. Around the dorsal edge and sides of the pharynx the
cut section of the dorsal mandible (d).

5. Projecting into the cavity of the pharynx on the ven-
tral or siphonal side, is a muscular, tongue-like body, the
odontophore, or the muscle of the lingual ribbon (k).

GENERAL ANATOMY OF THE SQUID. 357

(i.) On the pharyngeal or dorsal surface of this muscle
notice the teeth of the lingual ribbon. This consists, 1st,
of a delicate suh-radular membrane, which covers the sur-
face of the muscle, and 2d, of the radula, or series of
chitinous teeth, which project into the cavity of the pha-
rynx. In a cross section these teeth are seen to be of
two kinds, 1st, a central, symmetrical tooth, the rachidian
tooth, which, with the rachidian teeth above and below it,
forms the rachis of the lingual ribbon, and 2d, on each
side of this a series of three lateral teeth.

c. In a section a little farther back notice that the cavity
of the pharynx is completely separated from that of the
lingual ribbon, and the outer angles of the pharynx are
folded to form the superior salivary glands.

d. In a section through the eyes, notice : —

1. The small oesophagus (Fig. 188, c), with its epithelial
lining raised to form longitudinal folds, which are seen, in
cross section, as little papillae projecting into its cavity.

2. Ventral to the oesophagus, and enclosed in a common
sheath with it, the ducts of the two inferior salivary
glands.

3. On the middle line of the body, between the oesopha-
gus and the ventral surface of the head, the cross section of
the heart-shaped pedal ganglia (Fig. 188, d), which con-
sist of a central axis of white nerve fibres, and a peri-
pheral layer of gray matter, or ganglion cells.

4. Around the periphery of the ganglion notice the nerve
commissures (e,f), which pass from the arms into the
ganglia. Notice that they pass through the gray layer of
ganglion cells into the central white matter.

5. On the sides of the head notice the transverse sections
of the eyes.

6. The eye consists of an anterior chamber (m), and a

358 HANDBOOK OF INVERTEBRATE ZOOLOGY.

posterior chamber (k), separated from each other by the
lens (I).

(i.) The anterior chamber opens in Loligo to the exte-
rior by a small orifice (Fig. 176, c), situated at the ante-
rior angle of the eye.

FIG. 188.

FIG. 188. — Section through the head and eyes of a young specimen
of Loligo Pealii; magnified about twenty diameters. (Drawn from na-
ture by W. K. Brooks.)

a. Dorsal muscles of -head. b. Ventral muscles of head. c. (Esopha-
gus and salivary ducts, d. Pedal ganglion, e. Nerve commissures to
brachial ganglia. /. Nerves to muscles of head. ;/. Optic ganglion.
h. Ganglionic layer of retina, i. Layer of rods of retina, k. Posterior
chamber. 1. Lens. m. Pupil, n. Ciliary ganglion, o. Cornea, p. Iris.
r. Cartilaginous capsule of eye.

(ii.) The outer wall of the anterior chamber, in Loligo,
is formed by a transparent cornea (Fig. 188, o), which is
part of the general integument of the body. In Omma-
strephes the cornea is represented by two movable lids,
and the anterior chamber opens directly into the water.

(iii.) Inside the cornea a circular fold (p) runs forwards
over the ball of the eye, to form the iris, which surrounds

GENERAL ANATOMY OF THE SQUID. 359

a central opening, the pupil (m) . The posterior surface
of the iris is covered with a layer of epithelial cells, filled
with black pigment.

(iv. ) The lens (7) lies behind the pupil, and separates the
anterior chamber from the posterior. It is divided by a
deep equatorial groove into a small anterior portion, which
projects into the anterior chamber, and a much larger
portion, which lies in the posterior chamber. It is held
in place by the ciliary body (w)> which runs into the
groove between the two divisions of the lens.

(v.) The ciliary body is thin near the centre of the eye,
but peripherally it becomes thick, and contains a ciliary
ganglion (71), which consists of large granular nucleated
ganglion cells. The posterior or internal surface of the
ciliary body is covered by a layer of black pigment.

(vi.) The posterior chamber (&) is filled, in the living
animal, by the transparent vitreous humor, but in preserved
specimens the vitreous humor is somewhat opaque, finely
granular, and shrunken, filling only a small part of the
chamber.

(vii.) The sides and back of the posterior chamber are
formed by the retina (Fig. 188, /*, i). This is of nearly
uniform thickness, and it ends abruptly around the ante-
rior edge, where it joins the ciliary body. It consists of
three layers.

( viii. ) The inner layer (i) will be seen to be marked by fine
parallel striations, perpendicular to the surface of the eye-
ball. Examination with higher power will show that this
striation is produced by fine lines of black pigment, which
run inwards to the posterior chamber. Between the lines
of pigment are the transparent rods, which compose the
greater part of this layer. On the surface of the posterior
chamber the ends of the rods are covered by a delicate
layer of black pigment.

360 HANDBOOK OF INVERTEBRATE ZOOLOGY.

(ix.) The outer layer (A) of the retina is about as thick as
the layer of rods, and is made up almost entirely of gan-
glion cells, and is similar, in structure, to the surface layer
of the pedal ganglion (<Z).

(x.) The inner layer of rods is separated from the outer
layer of ganglion cells by a thin third layer, the layer of
pigment. This is continuous at the anterior edge of the
retina with the layer of pigment on the internal surface of
the ciliary body.

(xi.) Outside the retina there is a layer (?•) of cartilage
and muscular fibres, which supports the retina.

(xii. ) Outside this is the optic ganglion (g) . In the more
anterior sections this ganglion is small, and consists almost
entirely of gray matter, but in sections farther down the
head it is very large, and consists, like the, pedal ganglion,
of an outer layer of gray ganglion cells, and a central axis
of white nerve-fibres, some of which pass through open-
ings in the cartilaginous eye-capsule (r) into the ganglionic
layer of the retina.

e. In a section just posterior to the eyes (Fig. 189) no-
tice the oesophagus (Z), surrounded by a sheath of circular
fibres, which also enclose the ducts of the salivary glands.

1. Dorsal to this the middle line of the body is occupied
by the cerebral ganglia (m), and the commissure (g) be-
tween the optic ganglia.

2. The sides of the head are filled by two great masses, —
the optic ganglia (h) . Each of these consists of a surface-
layer of gray ganglion cells (J), of a second thin layer
of white matter (?'), and of a great central mass of white
matter (/*) in which are complicated radiating bands of
ganglion cells.

3. On the ventral surface of the oesophagus, on the mid-
dle line of the head, the pedal ganglion (/").

GENERAL ANATOMY OF THE SQUID. 361

4. Outside the brain and inside the integument of the
head notice the cut surfaces of the upturned edges of the
head cartilage (e, k).

FIG. 189.

FIG. 189. — Transverse section through the head of a young specimen
of Loligo Pealii; magnified about twenty diameters. (Drawn from nature
by W. K. Brooks. )

«. Circular muscles of siphon, b. Cavity of siphon, c. Longitudinal
muscles of siphon. tZ. Venae cavae. /. Pedal ganglion, g. Optic com-
missure, h. Optic ganglion, i. Peripheral layer of white matter.
j. Peripheral layer of gray matter. I. (Esophagus, m. Cerebral ganglion.
e, k. Cephalic cartilage.

5. On the ventral surface of the head notice the section
of the upper end of the siphon (b), the wall of which con-
sists of longitudinal muscles (c, c, c) and circular muscular
fibres (a).

362

HANDBOOK OF INVERTEBRATE ZOOLOGY.

6. Between the siphon and the brain the cut sections of
the anterior venae cavte (d).

f. In a section through the base of the head (Fig. 190)
notice : —

1. The mantle (m) separated from the head and siphon
by the mantle-cavil v.

FIG. 190.

FIG. 190. — Transverse section through base of head of young speci-
men of Loligo Pealii; magnified twenty diameters. (Drawn from nature
by W. K. Brooks.)

a. Retractor muscle of head. c. (Esophagus, d. Visceral ganglion.
e. Ear capsule. /. Siphon, g. Cephalic cartilage, h. Siphonal cartilage.
i. Mantle cartilage. /. Neck cartilage, m. Mantle, n. Pen and pen
sac.

GENERAL ANATOMY OF THE SQUID. 363

2. On the dorsal median line, the upper end of the
pen (w) in its sac.

3. Opposite this, on the dorsal surface of the head, the
neck cartilage (/).

4. Ventral to this the retractor muscle of the head («).
On the middle line, near the dorsal surface of the head,
the O3sophagus (c) , with a salivary duct on each side of it.

5. Ventral to the oasophagus the cross section of the vis-
ceral ganglion (d), which consists of a central axis of white
matter, and a thick peripheral layer of gray matter.

6. Around the oesophagus and visceral ganglion the ce-
phalic cartilage (</, </), which differs in form in different
sections. It forms a concave tray or box, which supports
the brain, and folds up around it at its edges.

7. Ventrally to the visceral ganglion the ear-capsule (e),
— a large hollow with vertical ridges of cartilage project-
ing into it from the sides. In a favorable section the ear-
capsule will bo seen to contain a second capsule of large
ciliated cells, outside which are scattered ganglion cells.
In a section through the anterior edge of the ear-capsule
the auditory nerve may be seen to pass from the visceral
ganglion into the ridge on the dorsal surface of the cap-
sule.

Other sections may show the nerves which pass from
the visceral ganglion to the siphon, and to the ganglia
stellata.

8. On the ventral median line between the ears and the
siphon, notice the single anterior vena cava, which has
been formed by the union of the two which are found in
more anterior sections.

9. Notice the cross section of the siphon, with its two
cartilages (A) fitting around the cartilaginous ridges (i) on
the inside of the mantle.

364 HANDBOOK OF INVERTEBRATE ZOOLOGY.

XXX.— THE DEVELOPMENT OF THE SQUID.

(Loliyo Pealii.)

THE eggs of the sea-urchin present an illustration of
total regular segmentation ; and those of a lamellibranch
illustrate total irregular segmentation. The eggs of the
squid may be examined as examples of partial segmen-
tation.

The eggs of the common squid are frequently taken in
the trawl or dredge, and they are often found among the
contents of a seine which has been drawn over :i weedy
bottom. They are also found occasionally on the beach,
among the sea-weeds which have been washed ashore.
They are contained in a cluster of elongated, spindle-
shaped, transparent egg-capsules, each of which contains
from twenty to seventy or eighty eggs. The capsules are
all joined to a central stem, thus forming a cluster, some-
thing like a bunch of grapes, and six or eight inches long.
Freshly-deposited eggs are not found as frequently as par-
tially-developed ones, and in the latter the little squid can
readily be seen, moving about within the egg-shell.

The newly-laid egg is surrounded by a transparent,
elastic, oval egg-shell (Fig. 191, a), with an opening, the
micropyle, m, at one end. Outside the egg-shell is the
gelatinous substance of the capsule, and inside, the elon-
gated oval yolk floats, suspended in a transparent albumi-
nous fluid. At first sight the yolk appears to be homoge-
neous, but careful examination shows that it is filled with
oil drops of various sizes, and with faintly marked edges.

Before the egg is laid the end of the yolk nearest the
micropyle becomes different from the rest. Its oil drops
disappear, it becomes transparent, finely granular, and

THE DEVELOPMENT OF

365

forms the germinative area of the egg, a little protoplas-
mic cup, which rests upon one end of the large yolk. In a
few hours the process of segmentation divides this cup up
into a layer of cells, the blastoderm (Fig. 191, c). It is
rather difficult to find the early stages of segmentation,
but the process is as follows : a groove or furrow makes
its appearance on the surface of the germinative area, and
divides it into halves. A second furrow, at right angles
to the first, then divides it into quarters, and two more
into eighths, and so on, until it is divided up into a
number of wedge-shaped cells, with their pointed ends
meeting at the centre, and their broad ends at the periph-
ery of the germinative area. The tips of the central
ends are then segmented off, as a central ring of small
cells, another ring is formed outside the first, and so on,
and the cells which are thus formed are also divided up
into smaller ones. In this way the germinative area is
cut up into a layer of blastoderm cells,
as shown in Fig. 191, with the bases
of the wedge-shaped cells, or segmen-
tation pyramids around its edge.

FIG. 191. — An egg in which the process of
segmentation is somewhat advanced. (Drawn
from nature by W. K. Brooks. )

a. Egg-shell. 6. Space between the shell
and the yolk, filled with transparent albumen,
c. Cap of segmentation spherules, m. Micro-
pyle.

FIG. 191.

The cells of the blastoderm are not very well marked
in a living egg, but when treated with borate of carmine,
to which a very small quantity of one-tenth per cent solu-
tion of osmic acid has been added, they become very con-
spicuous. Fig. 192 represents the edge of the blastoderm

366 HANDBOOK OF INVERTEBRATE ZOOLOGY.

of the e<™ shown in Fig. 191, after it has been thus treated.

.*,** O

The centre of the germinal area is occupied by a number
of small spherules which are irregularly spherical, and
each of which contains a very large nucleus.

As we pass from the centre of the. cap towards the pe-
riphery, the spherules become larger, and at its growing
edge they are replaced by large flattened pyramids (I, b),
which radiate out on all sides, upon the surface of the
yolk («), and gradually pass into the surface of the yolk,
without any distinct boundary at their outer ends.

FIG. 192. — More highly magnified view
of the growing edge of the blastoderm of the
egg shown in Fig. 1!H. after staining with
osmic acid and borate of carmine. (Drawn
from nature by W. K. Brooks. )

a. Unst'gmented yolk. h. Segmentation
pyramids. <•. First r<>\\ of cells, which have
been formed by separation from the ends of
the pyramids. </. Second set of cells, which
have been formed by the division of cells

like c. d'. Third set, similar to d. d". Fourth set, similar to d

and d'.

Careful examination shows that the segmentation spher-
ules are pretty regularly arranged with reference to these
pyramids. Just inside the broad inner ends of the pyra-
mids, there is a ring of large spherules (r), equal in num-
ber to the pyramids, and presenting every indication of
having been just formed by the separation of the proximal
end of each pyramid from the larger distal portion. In-
side these there is a second ring of spherules ((/'), about
half as large, and exactly twice as numerous as the first
set, and so placed that a pair of the spherules of the
second set are pretty nearly in a straight line with one of
the first set and the base of a pyramid. Each pair of this

THE DEVELOPMENT OF THE SQUID. 367

set is obviously the product of the division into two of a
spherule like those of the set (c), formed by separation,
somewhat earlier, from the end of a pyramid. Inside this
set is another series (rf"), equal in number to the set (dr),
and arranged like this set, in pairs along the radii which
end in the pyramids. Inside there is another set (d'"), of
the same kind, so that, as we pass inwards in the line of
each pyramid continued, we have the following series :
1. the pyramids; 2. one large spher-
ule (c); 3. two spherules (d'); 4. two
spherules (d") ; 5. two spherules (d'"},
and so on.

FHI. 19.']. — View of the anterior surface of an
embryo about two days old. (Drawn from nature
by W. K. Brooks. )

Hi. Mantle. s. Shell area. si'. Lateral
siphon folds, e. Eye. y. Yolk. b. Growing
edge of blastoderm.

In about two days the embryo is in the stage shown in
Fig. 193, and the positions of many of the organs of the
future squid are now indicated. The blastoderm has
grown down around the yolk, which is now entirely cov-
ered by it, except at the point (y), opposite the point where
segmentation began. The growing edge of the blastoderm
is marked by a ridge (b), which is ciliated. The em-
bryo is now bilaterally symmetrical, with reference to a
plane through the long axis, and the blastoderm has be-
come raised into a circular area, the mantle (w), at the
end where segmentation began. In an anterior view (Fig.
193), there is an elevated pad, the eye-stalk (e) on each
side of the body, and when one of these is seen in surface
view, a little pit, or invagination in its centre, will be
seen ; this is the chamber of the eye. Between the eye

368

HANDBOOK OF INVERTEBRATE ZOOLOGY.

and the mantle there is a little ridge (si), the inner
siphon fold.

In a day or so more the mantle (Fig. 194, m) is sharply
defined, and begins to overhang the mantle-cavity, under
which the rudimentary gills (g) have appeared as little
papillae covered with cilia. They are very similar in struc-
ture to the embryonic gill-tentacles of a lamellibranch. In
the centre of the mantle there is a small pit, the shell-
gland (s), in which the shell or pen
soon appears, as a little flat, trans-
e$ parent, circular plate (Fig. 195, s).

FiG. 194. — Foreshortened dorsal view of
the posterior surface of the embryo shown in
Fig. 193. (Drawn from nature by W. K.
Brooks. )

y, s, and ?». as in the preceding figure.
es. Eye-stalk. g. Gills. er. Otocysts.
si. Inner siphon-folds, a. Arms.

Fio. iw.

The eye-stalks (Figs. 194 and 195, es) now project con-
siderably from the sides of the dorsal end of the body.
The eye invaginations are well developed, and their open-
ings have begun to close up, to form the pupils, in which
the lenses are soon developed. In Fig. 195 the left eye is
shown in surface view and the right in profile. The
lateral siphon-folds (sif) are well developed, and the two
internal siphon-folds (Fig. 194, si) have appeared on the
posterior surface of the body. Opposite the outer ends
of the inner siphon-folds the ears (er) are now present as
two spherical pits, with wide mouths. On the anterior
surface, the mouth (Fig. 195, mo) is now visible, and a
short oesophagus runs inwards and upwards from it towards
the dorsal surface, but soon ends blindly. On each side

THE DEVELOPMENT OF THE SQUID.

369

of the mouth there is a very faintly-marked undulating
line of cilia, the velum (v).

Three pairs of rudimentary arms (a) are now present
upon the sides of the body, about half- way between the
mantle and the opposite pole of the egg. The yolk is now
entirely surrounded by the blastoderm, and has departed
still further from the regularly curved shape of Fig. 191.
The prolongations into the mantle and the eye-stalks are
well defined, and the portion of the yolk contained within

FIG. 195. — Embryo a little older
than the one shown in Fig. 19:], repre-
sented with its dorsal surface above, and
showing the anterior surface of the
body, as seen from the leftside. (Drawn
from nature by W. K.. Brooks. )

The letters of reference have the
following significance in all the figures
which follow: —

". Arms. a. Posterior or siphonal
pair of arms. a". Second pair,
a". Third pair. c. Eyes. er, Oto-
cyst. es. Eye-stalk. /. Fins. g. Gills.
h. Branchial hearts. m. Mantle.
mo. Mouth, re. Rectum, si. Inner
siphon-folds. */'. Lateral siphon-folds.
KIH. Siphonal muscle. v. Velum.
;//. Yolk. //'. External yolk-sac. ?/''. Yolk mass of the eye-stalks and
head. ?/"' and ?/' ". Yolk masses of the body and mantle.

the body of the embryo, which is not quite half the whole,
is separated by a well-marked constriction, just dorsal to
the arms from the remainder, which is now nearly spheri-
cal. The thin layer of blastoderm which covers this ex-
ternal portion of the yolk is split into two layers, separated
from each other by a cavity which is largest along the
median plane of the body, and which is traversed by a
few branched corpuscles, by the contraction of which,

FIG. 195.

370

HANDBOOK OF INVERTEBRATE ZOOLOGY.

rhythmical waves of the outer layer are set in motion
on the surface of the yolk. The fact that the mouth is
dorsal to the row of arms at this period is worthy of
notice.

The next figure (Fig. 196) is a view of the poste-
rior surface of a somewhat older embryo, represented,
with its dorsal surface below. The mantle (m) now
overhangs the body considerably at the sides, as well
as posteriorly, and the portion of the yolk which pro-
jects into it is more sharply marked off than before,
and is drawn out to a point at the dorsal end. The eye-
stalks (es) and their yolk protuberances, are much more
prominent, and the constriction which separates the body
from the external yolk is much more marked. The three
pairs of arms are a little larger than before, and a cavity
is visible in each of them. The inner siphon-folds (*/)

have lengthened, and their outer
ends now point towards the outer
folds (-«''), from which, however,
they are still widely separated.
The most important differences be-
tween this and the preceding stage
are differences of proportion and
a relative size, which are sufficiently
well shown in the drawings, and
do not call for description.

FKJ. 106. —The posterior aspect of an
older embryo, with its dorsal surface below.
(Drawn from nature by W. K. Brooks.)

For explanation of letters see Fig. 195.

Fig. 197 is a posterior view of an older embryo, figured
with its dorsal surface below instead of above, in order to

THE DEVELOPMENT OF THE SQUID.

371

facilitate comparison with the figures which follow, and
with the adult animal. The mantle (ni) has extended its
edge sufficiently to form a very well defined mantle-cavity,
within which the bases of the gill tentacles (g) are now
contained. The tail tins (f) have made their appearance
upon the dorsal surface of the mantle, and the rectum (re)
is now present as a raised, longitudinal, hollow rod, upon
the median line of the posterior surface between the gills.
The two inner siphon-folds (si) have met upon the middle
of the body, and their free edges have bent towards each
other to form the opening of the siphon ; but they have
not yet united with each other, and the siphon has the
characteristics of that of the adult Nautilus. The inner
folds are still separated from the outer ones (si'), but
the latter have begun to bend around upon the posterior
surface of the body. The eye-
stalks (es) are now extremely prom-
inent and conspicuous, and the yolk
protuberances no longer entirely fill
them, but have begun to decrease in
size, thus leaving between the eye
and the yolk a space in which the
optic ganglion has made its appear-
ance.

*Fio. 197. — A similar view of an older em-
bryo, with its dorsal surface below. (Drawn
from nature by W. K. Brooks. )

For explanation of letters see Fig. 195. FIG. IDT.

The three pairs of arms (a) are much elongated, and
begin to bend away from the surface of the yolk, which is
now divided into three well-marked regions : the external
yolk (y7), the portion within the head-region and eye-

372

HANDBOOK OF INVERTEBRATE ZOOLOGY.

stalks (y")> and the portion within the body and man-
tle (>/'")• During its development the embryo has under-
gone an increase in si/e, and although the drawing is less
enlarged, the embryo shown in Fig. 197 is actually much
larger than that shown in Fig. 194. The external yolk-
sac shares, in this growth, and is very much larger at a
somewhat later stage than the whole egg was at the begin-
ning of the process of development.

Fig. 198 is a view of the posterior surface of an em-
bryo somewhat older than in Fig. 197. The external
yolk-sac (y) has grown so much larger that only a small
part of it is shown in this and the next three figures. The
mantle (m), has grown so much that the gills (</), and
the rectum are nearly contained in the mantle-cavity. A
constriction across the base of each gill has separated the

branchial heart (/*), from the gill
proper. The inner folds (si) of
the siphon, have united with each
other to form the closed siphon
tube, and the inner and outer
folds (si, si'), have met and are
uniting with each other.

- es

Flo. 10S.

FIG. 198. — The posterior surface of
an older embryo, as seen from the ri^ht
side, with the dorsal surface below.
(Drawn from nature by W. K. Brooks.)

For explanation of letters see Fi.ir.
195.

The walls of the otocysts, (er), have grown thin, and
their cavities have greatly enlarged; the otoliths have
made their appearance, and the two chambers have begun
to move towards the median line, under the end of the
siphon.

THE DEVELOPMENT OF THE SQUID. 373

The external openings of the otocysts have become
constricted to long, tortuous, ciliated ducts, which are not
visible with a low power, and are not shown in the figure.

The eye-stalks, (es), are of about the same relative
length as in the last figure, but the yolk prominences
which have filled them up to this time are now almost
entirely withdrawn or assimilated, and the cavity of the
eye-stalk is nearly filled by the ball of the eye (e) , the
optic ganglion, and the white body.

The arms have lengthened, and suckers have appeared
upon the longest pair (a"), and a new pair (a'), have
made their appearance upon the posterior or siphonal sur-
face of the body.

The yolk is now divided into four well-marked regions,
the external yolk sac (y1), which is still nearly spherical;
the head yolk, which is pretty nearly cylindrical, and
which passes gradually into the external yolk sac ; the
body-yolk, much smaller than the head-yolk, and sep-
arated from it abruptly by a well-marked change of
outline ; and the little mass of yolk, at the dorsal end
of the body, constricted off from the mass by a deep
groove.

Fig. 199 represents a view of the posterior surface of a
somewhat older embryo.

The mantle is now large and bowl-shaped, and covers
the greater part of the body dorsal to the eye-stalks.
Chromatophores now begin to make their appearance
around the posterior side of the edge of the mantle, and
those which first appear are of a dark brown color.

The gills (g), have lengthened considerably, and are
divided by constrictions into a series of enlargements, the
dorsal one being much larger than the others, and be-
coming the branchial heart. The inner and lateral folds

374

HANDBOOK OF INVERTEBRATE ZOOLOGY.

of the siphon have completely united with each other,
and at the point of union the siphon is also united to the
body Avail, and the retractor muscle of the siphon (Fig.
198, .sm), now runs back to unite with the inner anterior
surface of the mantle. The otocysts have almost met each
other upon the median line, under the siphon, and their
walls are now very thin. The eye-stalks are prominent
at this stage, but they soon begin to
disappear.

The embryo shown, from the right
side, in the next figure (Fig. 200),
has assumed the general form of the
adult, and the eye-stalks have almost
disappeared, although, as shown in a
posterior view (Fig. 201), the eyes
are very prominent still, and are di-
rected more toAvards the ventral sur-

m -mz^-gm. r face than they are in the ;idult>

FIG. 199. — Posterior surface of a somewhat
older embryo. (Drawn from nature by \V. K.
Brooks. )

e. Eye. i. Ink bag. r. Rectum. The other
letters as in Fig. 195.

The mantle now covers about gone-half -the entire length
of the embryo, exclusive of the yolk-sac, and the neck-
cartilage (nc), has made its appearance, forming a support
for the edge of the mantle, on the middle line of the ante-
rior surface of the head. The posterior surface of the
mantle is now pretty well covered with ehromatophores,
which at this stage possess remarkable power of expan-
sion and contraction, and render the living embryo a very
beautiful and wonderful sight under a low magnifying

THE DEVELOPMENT OF THE SQUID.

375

power. They are, as yet, entirely absent from the ante-
rior surface of the mantle.

About this time small polygonal areolations, much like
epithelial cells, begin to make their appearance on the
posterior surface of the mantle, and soon spread over the
whole mantle, except the middle line of the anterior sur-
face, as shown in the figure. At a later stage (Figs. 201

FIG. 200.

FIG. 200. — A somewhat older embryo, seen from the right side. The
external yolk is now so large that only part of it is shown in the figure.
(Drawn from nature by W. K. Brooks.)

a', a", a"', «''". The four arms of the right side. /. The fin. g. The
gill. }>. The branchial heart, in. The free edge of the mantle, nc. The
neck cartilage, si. The siphon-tube, si". The lateral chamber of the
siphon, v. The valve of the siphon, x. The space between the integu-
ment and the surface of the external yolk, y', y,'y''', y'''. The four
divisions or regions of the yolk.

and 202), they cover the head and arms, as well as the
mantle, and still later they make their appearance upon
the surface of the siphon.

Upon cursory examination, they resemble epithelial cells
so much that they might readily be mistaken for them ;
but when more carefully examined with a high power,

370 HANDBOOK OF INVERTEBRATE ZOOLOGY.

they are seen to be due to the presence of minute branch-
ing tubes, which, spreading over the surface of the body
and inosculating, divide it up into small polygonal
areas.

\o fluid can be seen to circulate in them, but as they
appear at about the same time with the larger blood-
vessels of the surface of the body, they are probably the
indications of a system of capillary vessels.

The course of the larger blood-vessels on the posterior
face of the mantle is shown, at a somewhat later stage, in
Fig. 201. A large vessel will be seen to enter the mantle
on the median line near the dorsal end of the body. This
is the pallial artery from the systemic heart. Passing
forwards, it divides into three branches ; a pair of large
ones, and a median unpaired smaller one. The latter runs
forward, nearly to the lower edge of the mantle, and
divides up into a Dumber of smaller branches. The two
larger branches diverge, and running out towards the free
edge of the mantle, give rise, on their inner edges, 'to a
number of irregular branches, and on their outer edge-, to
a number of nearly parallel trunks, which communicate
with a pair of large venous trunks, each of which receives
:i .-mailer trunk from the median tract of the mantle, and
then, bending around the side of the body, runs inwards
to open into the larger vena cava, from which the blood
]>u-ses into the branchial heart, and is conveyed to the
gills. The branchial hearts appear at quite an early stage
of development, but the systemic heart is not developed
until about the stage shown in Fig. 201. During the later
stages of development, and in the adult also, the small
size of the gills is no doubt compensated, to a great de-
gree, by the aeration of the blood while it is passing
through the system of vessels near the exposed surface of
the mantle.

THE DEVELOPMENT OF THE SQUID.

377

At the stage shown in Fig. 200, the siphon has sub-
stantially its adult form, and is made up of two lateral
chambers (si') , which have been formed from the lateral
siphon folds, and which open into
the mantle-chamber, but have no
external openings ; and a single
median chamber («'), on the poste-
rior surface of the body, which has
been formed by the union of the
two inner siphon folds, and which
opens into the mantle-chamber as
well as externally.

At the point where the lateral
chambers meet the median cham-
ber, the wall of the siphon is united
to the wall of the body, and the
three chambers are thus shut off
from communication with each
other.

FIG. 201. — A free swimming squid, with
the external yolk almost absorbed. (Drawn

from nature by W. K. Brooks. )

x* i ( J . - ( ' i .
Thj letters as in the preceding figures.

The animal is so perfectly transparent that the valve-
like action of the two outer chambers can be perfectly
seen, as their free inner edges are thrown out against the
mantle so as to close it at each contraction, and the water,
which passes in around the whole free edge of the mantle,
is thus concentrated in the funnel-shaped middle chamber
of the siphon.

At about this time the valve of the siphon (Fig. 200, v),
is developed as a single unpaired flap, which arises from
the posterior surf:iee of the nerk.

378

HANDBOOK OF INVERTEBRATE ZOOLOGY.

Considerable change has now taken place in the shape
of that portion of the yolk which is contained in the head.
It is reduced to a long, narrow tube (y"), which connects
the portions contained in the body proper (//", y""), with
the external yolk sac (.y')- The pulsatile space (x), be-
tween the outer wall and the surface of the yolk sac, is
more plainly shown in this figure than in the preceding
ones, although a profile view shows it with equal distinct-
ness at earlier stages.

Fig. 202 is a posterior view
of an embryo a little older than
the one shown in Fig. 201. A
large rounded prominence on
each side of the head marks the
position of the eye-stalk, and the
eyes are farther forward than
they are in older specimens, but
in other respects the form is very
similar to that of the adult. The
ink sac (i) has appeared, and is
filled with ink, and the tip of the
free portion of the rectum is pro-
longed at its corners into the pair
of ear-like anal valves.

FIG. 202. — A free swimming squid,
with the external yolk entirely ab-
sorbed. (Drawn from nature by W. K.
Brooks. )

The letters as in the preceding fig-
ures.

There are considerable individual variations in the ar-
rangement of the chromatophores, but there are certain

THE DEVELOPMENT OF THE SQUID. 379

features which are observed in all the specimens, and
which seem to be constant.

The first which make their appearance are dark brown
in color, and are placed in a ring of six or seven, (Fig.
202), around the edge of the mantle on the posterior
surface. They are a little smaller, and somewhat more
excitable than those which appear subsequently, and
they can be readily recognized in the later stages shown
in Figs. 201 and 202. They are soon followed by
larger spots of the same dark brown color, scattered
irregularly over the posterior surface of the mantle (Fig.
202).

The next spots to appear are upon the arms, and are
also dark brown. At first there are two upon the first or
siphonal pair of arms, and three upon the second pair
(Fig. 199). A fourth soon appears upon the second
arm, and these four remain conspicuous until quite a
late stage of development (Fig. 202). Three large
brown spots now appear upon the posterior surface of
the head (Fig. 199), and they are soon followed by
others.

A second set of spots, more deep-seated and of a bright
orange color, soon make their appearances, and are much
more constant in position than the brown ones. The first
pair which appear are just in front of, or ventral to the
eves. They are soon followed by a single one on the
middle line of the head, at the bases of the first pair of
arms, and another single one on the middle line of the
edge of the mantle. About the same time a pair appear
dorsally to the eyes, and another pair on the edge of the
mantle, near the sides.

Four small orange spots next appear upon the second
pair of arms (Fig. 202, a"), alternating with the four

380 HANDBOOK OF INVERTEBRATE ZOOLOGY.

larger brown spots, and, soon after, a ring of six or eight
orange spots appears on the mantle, dorsal to the ink bag.
Two orange spots next appear upon the first pair of arms
(Fig. 202, a'), alternating with the brown spots.

INDEX.

Ah-actinal area of Starfish, 57 ; of Sea
Urchin, 83.

Abdomen of Anodonta, 276, 285 ; of
Crab, 171 ; of Crab Megalops, 220,
217 ; of Crah Zoea, 20" ; of Cyclops,
225, 220, 230 ; of Grasshopper, 238,
250 ; of Crayfish, 185, 186 ; of Lob-
ster, 186.

Abdominal artery of Crab, 185 ; gan-
glia of Grasshopper, 264.

Ab-oral surface of Starfish, 57; of
Sea Urchin, 83, 87; tentacles of
Starfish, 63, "5.

Act-tabula of Squid, 337.

Actinal surface of Sea Urchin, 83, 87 ;
of Starfish, .r>7.

Alveola of Sea Urchin, 95, 97.

Ambulacra of Sea U rchin, 84 ; of Star-
fish, 63, 69, 76.

Ambulacra! area of Sea Urchin, 88; of
Starfish, 60, 61; furrow of Star-
fish, 57; ossicle, 58, 61, 76, 88, 89;
pores of Sea Urchin, 88; pores of
Starfish, 60, 61; suture, 88; sys-
tem, 68, 69, 76; tube of Sea
I" rchin, 91, 98; tube ' of Starfish,
58, 78; vesicle of Sea Urchin, 91,
98 ; vesicle of Starfish, 69.

Amoeba, i. : contractile vesicle, 6 ;
ectosarc, 4 ; endoplast, 6 ; endosarc,
4; food vacuole, 5; pscudopodia, 4.

ArapulUe of Sea Urchin, 91, 98; of
Starfish, f>9.

Anal plates of Sea Urchin, 85.

Anal valve of Squid, 378.

Annuli of Leech, 160.

Anodonta, xxv. : abdomen, 276, 295 ;
adductor muscles, 272; arms, 274,
284; aorta, 281, 282 ; auditory organ,
281 ; auricle, 281, 282, 293 ; bile duct,
296; body-cavity, 286, 287, 289, 290,
293; Bojanus' organ, 281, 282,290,
293, 294, 295; branchial chamber,
274, 288, 291 ; branchial current, 27'2 ;
branchial siphon, 272; branchial slits,
277; byssus of larva, 331; cloa<-:il
chamber, 277, 288, 291 ; cloacal siphon,
272; digestive organs, 284; dorsal
edge, 271; epidermis, 271, 273; foot,
272, 276, 294, 295 ; general anatomy,
xx v. ; gills, 276, 277, 288, 200, 291, '2!»2 ;
integument, 287 ; intestine, 283 ;
287; heart, 281, 282, 293, 294;
hinge-ligament, 271 ; hinge-teeth,
273; labial palpi, 276; larva, 330;
lines of growth, 271 ; liver, 284,
296; mantle, 274, 287; mantle
chamber, 286, 288, 290, 291; man-
tle muscles, 274; mesentery, 290;
mouth, 276, 284; muscles, 290; pal-
lial line, 272; parasitism of larva,
332; parieto-splanchnic ganglia, 288;
pearly layer, 273 ; pedal ganglia, 296 ;
pericardium, 274, 281, 293 ; posterior
end, 271; prismatic layer; protrac-
tor muscles, 273; rectum, 274, 2S4,
286; renal organ, 281, 282; repro-
ductive organs, 296 ; retractor mus-
cles, 273; setae of larva, 332; shell,
271 ; shell of larva, 331 ; sinus veno-
sus, 294 ; siphon, 272 ; stomach, 284,
283 ; transverse sections, xxvi ; umbo,

382

INDEX.

271,; valve, 271; venous sinus, 282;
ventricle, 281, 282, 293; (see also
Lame Hi branch).

Antenna of Crab, 177, 181, 184, 185,
189; of Megalops, 217,218; of Zoea,
210,211; of Cyclops, 225,227,230;
of Grasshopper, 243; of Nauplius,
235.

Antennary gland of Crab, 204 ; fossa of
Grasshopper, 243; somite of Crab,
169 ; sternum of Crab, 183.

Antennules of Crab, 169, 177, 181, 182,
184 ; of Megalops, 217, 218 ; of Zoea,
210.

Anterior ray of Starfish, 57.

Anus of Anoclouta, 274, 284 ; of Crab,
174; of Crayfish, 187; of Earth-
worm, 141 ; of Grasshopper, 253, 262 ;
of Lamellibranch embryo, 329; of
Leech, 175; of Lobster, 187; of
Paramcecium, 11 ; of Sea Urchin, 85 ;
of Squid, 339; of Starfish, 65; of
Vorticella, 19; of Zoea, 209.

Aorta of Anodonta, 281 ; of Squid,
345, 347.

Apodemata of Crab, 181; of Grass-
hopper, 264.

Appendage of Crab. 175, 178, 182, 183 ;
of Cyclops, 227 ; of Nauplius, 236.

Aristotle's Lantern, 93, 95, 96 ; muscles
of, 97, 98.

Arms of Squid, 333, 336, 337, 369.

Auditory ganglion of Grasshopper, 266;
hairs of Crab, 206; nerve of Grass-
hopper, 265; nerve of Squic'., 363;
rods of Squid, 268 ; organ of Crab,
182, 206, 221; organ of lamelli-
branch embryo, 329; organ of Lob-
ster, 190, 223; organ of Grasshop-
per, 264; spindles of Grasshopper,
organ of Hydro Medusa, 55 ; organ
of Squid, 363, 372.

Auricle of Anodonta, 281, 282, 293.

Auriculae of Sea Urchin, 90, 98.

Basipodite of Crab, 176.

Beak of Squid, 333, 348. 355.

Bile duct of Anodonta, 296.

Bipinnaria, 130.

Biviiun, 58.

Blastoderm of Squid, 365.

Blastostyle, 49.

Blood of Earthworm, 146.

Blood-vessels of Earthworm, 143, 145;
of Crab, 165 ; of Starfish, 71, 77.

Body cavity of Anodonta, 286, 287,
289, 290, 293 ; of Hydroid, 33.

Bojanus' organ, 281, 282, 290, 293, 294,
295, 329.

Brachiolaria, 130.

Brain of Leech, 167,

Brain of Earthworm, 146.

Brain of Crab, 205.

Branchial area, 170; artery of Squid,
340, 343 ; chamber of Anodonta, '274,
288, 291; chamber of Crab, 193; cur-
rent of Anodonta, 272 ; heart of
Squid, 340, 343, 372 ; siphon of Ano-
donta, 272; slit of Anodonta, 277;
vein of Squid, 340, 345.

Branchiostegite, 188.

Buccal body of Squid, 348, 354.

Buccal pouch of Leech, 1G3, 164.

Bud-medusa, 50.

Budding in llydroids, 35; in Sponge,
25.

Byssus of Anodonta, 331.

Campanularian Hydroid, vi, viii.

Carapace of Crab, 169, 184 ; of Cray-
fish, 185; of Cyclops, 225; of Lob-
ster, 185 ; of Megalops, 217 ; of Zo-
ea, 207.

Cardiac; area, 170; pouch, 200.

Cardo, 246.

Carpopodite, -176.

Cement of Spermatophore, 233.

Cephalic area, 170.

Cephalothorax of Cyclops, 225; of
Crayfish, 185 ; of Lobster, 185.

Ccrcus, 252.

Cerebral ganglia of Crab, 205; of
Earthworm, 146 ; of Leech, 167.

Cervical suture of Lobster, 185.

Chela, 177.

Chromatophore, 334, 373, 379.

INDEX.

383

Chymiferous tubes, 41.

Cilia of Oyster embryo, 329.

Cilia of Paramoeciuin, 8.

Ciliary body, 359.

Ciliated funnel, 148.

Circulatory organs of Squid, 341.

Circum-oral water tube, 70, 93.

Cloaca of Sponge, 23, 24.

Cloacal chamber of Anodonta, 277,
288, 291; siphon of Anodonta,
272.

Clypeus, 243.

Coenosarc of Ilydroid, 32.

Colon of Grasshopper, 262; of Leech,
165.

Conjugation, 21.

Contractile vesicle of Amoeba, 6; of
Paramoecium, 11; of Vorticella, 19.

Cornea, 358.

Corona, 85.

Corpus adiposum, 259.

Coxa, 240.

Coxopodite, 176.

Crab, abdomen of, 171 ; abdomen of
Megalops, 217, 220; abdomen of
Zoea, 207, 214 ; anatomy of, xx ; an-
tenna of, 169, 177, 181, 184; an-
tenna of Megalops, 217, 218 ; anten-
na of Zoea, 210, 211 ; antennary
gland of, 204; antennary sternum of,
183 ; antennule of, 169, 177, 181, 182,
184 ; antennule of Megalops, 117, 118 ;
x antennule of Zoea, 209, 210 ; anus of,
174; anus of Zoea, 214; apodemataof,
1S1 ; appendage of, 175, 178, 182, 183 ;
auditory hairs of, 206; auditory organ
of, 182, 206, 221 ; basipodite of, 176,
180, 211; blood-vessels of, 195;
branchial chamber of, 193 ; carapace
of, 170, 184, 185; carapace of Mega-
lops, 217; carapace of Zoea, 207;
carpopodite of, 176; cerebral ganglia
of, 205 ; chela of, 177 ; coxopodite of,
176, 211; dactylopodite of, 176; di-
gestive organs of, 199 ; dorsal spine
of Zoea, 208; dorsal surface of, 169;
eggs of, 204 ; embryonic Zoea of, 214 ;

endognathal palp of, 176 ; endopodite
of, 175, 178, 180, 187, 211,213; epime-
ron of, 174, 184 ; epipodite of, 176, 178,
189; episternum of, 173, 184; epi-
stoma of, 183; exopodite of, 175, 178,

180, 187,211, 213; eye of, 169, 177,

181, 182, 184 ; eye of Megalops, 217 ;
eye of Zoea, 207 ; flabellum of, 176,
178, 196; flagellum of, 182; flancs
of, 184, 193 ; gastric ganglia of, 205 ;
gastric mill of, 203; gills of, 184,
193, 196; gills of Megalops, 207;
gnathostegite of, 176 ; hard parts of,
xviii ; heart of, 194 ; heart of Zoea,
209; intestinal coecum of, 201; in-
testine of, 201 ; intestine of Zoea,
209; ischiopodite, 176; labrum of
Zoea, 210, 211 ; lateral spine of Zoea,
208 ; liver of, 193, 194, 201 ; liver of
Zoea, 209; mandible of, 180; man-
dible of Megalops, 218 ; mandible of
Zoea, 210, 211; mandibular palpus
of, 181; maxilla of, 179, 180, 196,
198 ; maxilla of Megalops, 218 ; max-
illa of Zoea, 210, 211 ; maxilliped of,
175, 178, 196; maxilliped of Mega-
lops, 217, 219; maxilliped of Zoea,
210, 213, 214 ; Megalops stage of, 215 ;
mcropodite of, 176; metamorphosis
of, xxi; metastoma of, 180; muscles
of, 192; nervous system of, 205;
cesophageal commissure of, 205 ; ova-
ry of, 194, 204; oviduct of, 204;
pereiopod of, 175, 176 ; pereiopod of
Megalops, 217, 219; pereiopod of
Zoea, 214; pericardium of, 192;
peristome of, 179 ; pleopod of, 171 ;
pleura of, 173 ; propodite of, 176 ;
protopodite of, 176, 179, 187, 211;
pyloric coeca of, 201 ; rectum of
Zoea, 209; reproductive organs of,
204, 205 ; resemblance to lobster, 221 ;
respiratory organs of,195 ; rostral sep-
tum of, 183; rostrum of, 169; ros-
trum of Megalops, 217 ; rostrum of
Zoea, 207; scaphognathite of, 179,
180; scaphognathite of Zoea, 212;

384

INDKX.

seminal receptacle of, 'JO}; somite
of, 182; sternal plastron of, 171, 174,
183; sternum of, 173, 184; stomach
of, 190, 200; stomach of Zoca. 20! I;
telson of Megalops, 21? ; telson of
Zoea, 207, 214; terguni of, 17-5; tc>ti>
of, 205; thoracic ganglia of, 20(i;
vas defereus of, 177, 205; Zoea of,
207.

Cranium of Squid, 348.

Crayfish, hard parts of, xix (see Lob-
ster).

Crop of Earthworm, 145, 159 ; of Gra->-
hoppcr, 261 ; of Vorticella, 18.

Cuticle of Earthworm, 152, 159; of
Paramceciurn, 9; of Vorticella, 17.

Cyclas, gill of, 297.

Cyclops, xxii. : abdomen of, 225, '2'2\,
230; antenna of, 225, 227, 230; an-
tenna of Nauplins, 23."»; appendage*
of, 227 ; appendages of Xauplins 236 ;
carapace, 225 ; cephalothorax, 225 ;
digestive organs, 228; digeMive
organs of Xanplius 236 ; discharging
bodies of Spermatophore, 232 ; eye of,
225; fertilization of egg, 231; la-
brum of, 226; lahnim of Xauplius
234; male, structure of, 230; inau-
dible of, 227 ; maxilla of, 227; meta-
morphosis, xxii; metastoma of, 2'3> ;
mouth of, 226; Xauplius stage, 231;
ovary of, 229; oviduct of, 228,229;
ovisac of, 22(>; reproductive organs
of female, 228 ; reproductive organs
of male, 230; rostrum of, 225; seta-
of, 226; shell gland of, 220; sporma-
theca of, 229; spermatic duct of, 229;
spermatophore of, 232; spermatozoa
of, 233 ; style of, 226 ; testis of, 2:50 ;
thoracic appendages of, 228; thoracic
somites of, 225 : vas defercns of, 230.

Cyst of Vorticella, 22.

Dactylopodite, 176.

Development of Echinodcrms, xiv;
of Hydro Medusa, viii. ; of Crab, xxi. ;
of Lamellibranchs, xviii. ; of Sea
Urchin, 126; of Squid, xxv.

Digestive organs of Anodonta, 284 ; of
Crab, 199; of Cydopt, 228, 236; of
Earthworm, 143, 158; of Grasshop-
per, 259; of Leech, 163; of Paramee-
cium, 10 ; of Plutcus, 111, 114 ; of Sea
Urchin, 92, '.K5, !)l ; of Squid, 345; of
StarhMi, 63, 7-"' ; of Vorticella, 18.

Dip net, use of, 37.

Dipping tube, use of, 3.

Direction cell of Lamellibranchs, 319;
direction cell of Sea Urchin, 104.

Discharging bodies of spermatophore in
Cyclops, 232.

Dorsal spine of Zoea, 208; dorsal sur-
face of Crab, 169; dorsal vessel of
Earthworm, 145; dorsal vessel of
Grasshopper, 258.

Ear of Anodonta, 281 ; of Crab, 182,
206, 221; of Grasshopper, 264; of
Lobster, 190, 223; of Squid, 363,
368, 372.

Earthworm, xv., xvi. : blood of, 1 12 ;
blood vessels of, 143, 145; cere-
bral ganglia, 146; ciliated funnel,
14S; crop of, 145, 159; cuticle of,
152, 159; digestive organs of, 143,
158; gizzard of, 145, 159; hepatic
glands of, 145, 15!); hypc>derinis of,
154; integument of, 152; intestine of,
145, 159; microscopic structure, xvi. ;
muscles of, 143, 1.V2, 151,156; ner-
vous system of, 146, 148, 157; oesoph-
agus of, 144, 159; ovary of, 152; ovi-
duct of, 152; perivisceral thud of,
143; pharynx of, 143, 158; repro-
ductive organs of, 149 ; segincntal
organs of, 148, 149; seminal recepta-
cle of, 151 ; seminal vesicle of, 149;
setae of, 157; setigerons gland of,
152; testis of, 144, 149; tubular
band of, 158 ; vas dcferens of,
150.

Echinoderms, embryology and meta-
mprphosis of, xiv.

Ectoderm of Hydro Medusa, 46, 48;
of 'Lamelhbrauch, 322; of Sea
Urchin, 108.

INDEX.

385

Ectosarc of Amoeba, 4; of Paramce-
cium, 9 ; of Vorticella, 17.

Egg of Crab, 204 ; of Lamellibranch,
312; of Sea Urchin, 99; of Squid,
364.

Egg, direction cell of, 104, 319 ; ferti-
lization of, 100, 234, 314; germina-
tive pole of, 104 ; germinative
vesicle of, 102, 319 ; nutritive
pole of, 104; ovarian, 312; prin-
cipal axis of, 103; polar globule
of, 104, 319; resting stage of, 104,
321 ; segmentation of, 102, 318 ; seg-
mentation cavity of, 107, 322; seg-
mentation nuclei of, 105, 320 ; unfer-
tilized, 102, 312; yolk of, 103.

Embryology of Lamellibranch, xxviii. ;
of Oyster, 312; of Sea Urchin, xiv.

Encystment, 22.

Encloderm of Hydro Medusa, 44, 48 ;
of Hydroid, 32, 33 ; of Lamellibranch,
322 ; of Sea Urchin, 107 ; of Sponge,
29.

Endognathal palp, 176.

Endoplast of Amoeba, 6 ; of Paramce-
cium, 12; of Vorticella, 19.

Endopodite, 172, 175, 228.

Endosarc of Amoeba, 4; of Paramce-
cium, 9 ; of Vorticella, 16.

Epidermis of Anodouta, 271, 273.

Epicranium, 242.

Epimeron of Crab, 174, 184; of Grass-
hopper, 247 ; of Lobster, 187.

Epiphysis of Sea Urchin, 96.

Epipodite, 176.

Episternum of Crab, 173, 174, 184 ; of
Grasshopper, 248.

Epistoma of Crab, 183 ; of Vorticella, 15.

Exopodite, 173, 175, 228.

Eye of Crab, 169, 177, 181, 182, 184 ; of
Megalops, 217 ; of Zoea, 207 ; of Cy-
clops, 225 ; of Grasshopper, 243 ; of
Lamellibranch, 329 ; of Leech, 160 ;
of Lobster, 185, 189 ; of Squid, 358,
367, 368, 370.

Facial area of Carapace, 170.

Femur, 241.

Fission, 20.

Flabellum, 176, 182, 196.

Flagellum, 329.

Flanc, 184, 193.

Food vacuole of Amoeba, 5 ; of Para-
mcecium, 11; of Vorticella, 19.

Foot of Anodonta, 272, 276, 296; of
Grasshopper, 242 ; muscles of, 290.

Frontal lobe of Carapace, 170.

Furcula, 264.

Galea, 246.

Ganglion, abdominal, of Grasshopper,
264 ; auditory, of Grasshopper, 266 ;
brachial, of Squid, 354 ; cerebral,
of Anodonta; cerebral, of Crab, 205;
cerebral, of Earthworm, 146 ; cere-
bral, of Leech, 169; cerebral, of
Squid, 360; ciliary, of Squid, 359;
gastric, of Crab, 205; -gastric, of
Grasshopper, 263 ; gastric, of Leech,
167 ; Lamellibranch, embryo, 329 ;
ossophageal, of Grasshopper, 263;
optic, of Squid, 360; parieto-splanch-
nic, of Anodonta, 288 ; pedal, of
Anodonta, 276; pedal, of Squid, 357,
360 ; retinal, of Squid, 366 ; stellate,
of Squid, 338 ; stomato-gastric, of
Leech, 169 ; sub-oesophageal, of
Grasshopper, 264 ; thoracic, of Crab,
206; thoracic, of Grasshopper, 264;
visceral, of Squid, 363.

Gastric area of carapace, 170; coeca,
262; ganglia of Crab, 205; ganglia
of Grasshopper, 263; ganglia of
Leech, 167 ; mill, 202, 203.

Gastrula, 167.

Gastrula mouth, 107.

Gena, 244.

Genital chamber, 252.

Germinative pole of egg, 104 ; germi-
native vesicle, 102.

Gill of Anodonta, 276, 277, 288, 290, 291,
292 ; of Crab, 184, 193, 196 ; of Crab
Megalops, 217 ; of Lamellibranchiate,
xxvii.; of Squid, 340, 343, 368,373;
of Unio, 305 ; of tentacles of Mytilus,
300; of Uuio, 307.

386

INDEX.

Gizzard of Earthworm, 145, 159.

Glochidium, 331.

Gnathostrgitc, 170.

Gonangium,49.

Grasshopper, xxiii., rxiv. ; abdomen,
238, 250; abdomen of female, 254;
alxlomen of male, 251 ; abdomen,
metamorphosis of, 256; abdominal
ganglia of, 264; antenna of, 243;
antennary fossa of, 213 ; anus of, 253,
262; apodcmata of, 264; auditory
ganglion of, 266; auditory nerve
of, 265; auditory organ of, 264;
auditory rods of, 268; auditory
spindles of, 268 ; cardo of, 248 ; cer-
cus of, 252 ; colon of, 262 ; clypeus of,
243; corpi^ Hdiposum o£ 259; coxa
of, 240 ; crop of, 261 ; digestive organs
of, 259 ; dorsal vessel of, 258 ; ear of,
264; epicraniumof, 242; epimcronof,
249; episternum of, 248 ; eye of, 243 ;
femur of, 240 ; foot of, 242 ; furcula
of, 264 ; galca of, 246 ; gastric coeca
of, 262; gastric ganglia of, 263 ; gena
of, 244; genital chamber of, 252;
gula of, 245; hard parts of, xxiii.;
head of, 238, 242 ; heart of, 258 ; ilium
of, 262; iugluvics of, 261; internal
structure of, xxiv. ; intestine of, 202 ;
labial palpus of, 245; labium of, 245;
labrum of, 243 ; lacinia of, 246; leg
of, 240; ligula of, 245; malpighian
tube of, 262; mandible of, 244 ; maxilla
of, 246; maxillary palpus of, 246;
mentutn of, 245 ; mesosternum of,
248; metasternuin of, 248; metasto-
ma of, 245 ; nervous system of, 263 ;
occipital foramen of, 245; ocellus of,
243 ; a'sophageal ganglia of, 263 ;
oesophagus of, 261 ; ovariole of, 263 ;
ovary of, 263, oviduct of, 263; ovi-
positor of, 251, 256 ; palpiger of, 245 ;
patagium of, 250 ; podical plate of,253 ;
postscutellum of, 247 ; prescutum of,
247; pronotum of, 246; prostcrnmii
of, 247; prothorax of, 246; prove n-
triculus of, 261; pulvillus of, 242;

rectum of, 262; reproductive organs
of, 259, 263; salivary duet of, 261;
salivary gland of, 261 ; scutellum
of, 247; scutum of. 247; sperma-
theca of, 263 ; spiracle of, 249, 251 ;
stipes of, 216; Mib-gcnital plate of,
251 ; sub-mentumof, 245; sub-<i.-soph-
ageal ganglion of, 264; tarsus of,
242 ; tcgmina of, 238 ; thoracic gan-
glion of, 264; thorax of, 238, 246;
tibia of, 242 ; tongue of, 245 ; trachea
of, 259 ; troclianter- of, 240 ; tympa-
num of, 264; ungues of, 242 ; vagina
of, 263 ; ventral nerve chain of, 263 ;
ventrieulus of, 262; wing of, 238,
239; wing cover of, 238.

Gula, 245.

Head of Grasshopper, 233, 242; of
Squid, 333.

Heart of Anodonta, 281, 282, 293, 294.

Heart of Crab, 194; of Zoea, 209; of
Grasshopper, 258 ; of Sea Urchin,
94; of Starfish, 71.

Hectocotylus, 349.

Hepatic artery of Crab, 195 ; coeca of
Starfish, 63, 64, 75; duct of Squid,
348 ; glands of Earthworm, 145, 159 ;
lobes of Crab, 170 ; tubules of Crab,
201.

Hinge ligament of Anodonta,271 ; teeth
of Anodonta, 273.

Ilydranth, 32.

llydrocaulus, 32.

Hydroid — asexual form of, 30 ; body
cavity of, 33; budding in of, 35; coe-
nosarc of, 32 ; ectoderm of, 32 ; en-
dodcrm of, 33; hydrotheea of, 33;
lasso cells of, 34 ; manubrium of, 33;
medusa stage of, viii ; nematocysts
of, 34 ; pcrisarc of, 32 ; regeneration
in, 26; supporting layer of, 33.

Hydro Medusa, vii, viii ; auditory or-
gan of, 55; blastostyle of, 49; chy-
miferous tubes of, 41 ; ectoderm of,
45-48; endoderm of, 44-48; gonan-
gium of, 49 ; manubrium of, 41 ; me-
dusa buds of, 50 ; muscular layer of,

INDEX.

387

45-48; nervous system of, 46-48;
ocellate of, vii ; ocelli of, 42; otocyst
of, 55 ; otolith of, 55 ; reproductive
calycle of, 49; reproductive organs
of, 42 ; stomach of, 41 ; sub-umbrella
of, 39 ; tentacles of, 40, 41, 44, 45 ;
umbrella of, 39; velum of, 39.

Hydrorhiza, 32.

Hyclrotheca, 33.

Hypodermic of Earthworm, 154.

Ilium of Grasshopper, 262.

Imbedding, method of, 26, 27.

Incurrent ostia of Mytilus, 303 ; of Unio,
306.

Ingluvies,261.

Ink Bag of Squid, 339, 378.

Integument of Anodonta, 287; of Earth-
worm, 152, 154.

Inter-arabulacral area of Sea Urchin, 88;
of Starfish, 61 ; ossicles of Sea Urchin,
88, 89: ossicles of Starfish, 59, 61, 75.

Inter-lamellar junctions of Mytilus, 301;
of Unio, 310.

Inter-tentacular junctions of Mytilus,
301 ; of Uuio, 307.

Inter- radius, 57, 65.

Inter-radial partition, 62 ; sutures, 87.

Intestinal coecum of Crab, 201.

Intestine of Anodonta, 284, 287; of
crab. 201; of Zoca, 209; of Earth-
worm, 145, 159 ; of Grasshopper, 262 ;
of Leech, 163, 164; of Oyster em-
bryo, 329; of Sea Urchin, 92, 91 ;
of Squid, 339, 346 ; of Starfish, 65.

Iris of Squid, 358.

Ischiopodite, 17'i.

Jaws of Squid, 348.

Labial palpus of Anodonta, 276 ; of
Grasshopper, 245.

Labium of Grasshopper, 245.

Labrum of Crab Zoea, 210, 211; of Cy-
clops, 226 ; of Nauplius, 234 ; of
Grasshopper, 243.

Lacinia of Grasshopper, 246.

Lamellibranchs, xxvi, xxvii, xxviii (sec
also Anodonta, Cyclas, Mytilus, Oys-
ter, Unio).

Lamellibranchs, direction cell of, 319;
development of, xxviii; gill of,
xxvii ; ectoderm of, 322 ; ear of, 329 ;
eye of, 329 ; segmentation of egg,
319 ; seminal fluid of, 313 ; sperma-
tozoa of, 314.

Lasso cell, 34.

Lateral Spine of Zoea, 208.

Leech, xvii ; annuli of, 160 ; blood ves-
sels of, 165 ; brain of, 167; buccal
pouch of, 163, 164 , cerebral ganglia
of, 167 ; colon of, 165 ; digestive or-
gans of, 163 ; eyes of, 165 ; gastric
ganglia of, 167; intestine of, 163, 164 :
mouth of, 161,167; mucous glands
of, 162 ; nervous system of, 165, 166 ;
ovary of, 166 ; pharynx of, 163, 164 ;
proboscis of, 160; reproductive or-
gans of, 161, 162, 166; segmental or-
gans of, 162.

Leech, stomato-gastric ganglia of, 167 ;
stomach of, 163, 164 ; testis of, 166 ;
vagina of, 166; vesicula seminales
of, 166.

Leg of, Grasshopper, 240.

Lens of Squid, 358, 359.

Ligula of Grasshopper, 245.

Lines of growth, 271.

Lingual ribbon of Squid, 348.

Liver of Anodonta, 284, 296 ; of Crab,
193, 194, 201 ; of Crab Zoea, 209; of
Squid, 344, 347.

Lobster, xix, abdomen of, 186; anten-
nae of, 185, 189; antennulc of, 185,
189; anus of, 187; auditory organ
of, 190, 223; branchiostegite of, 188;
carapace of, 185; cephalothorax of,
185; cervical suture of, 185; epister-
num of, 187; eye of, 185, 189; max-
illa of, 189; maxilliped of, 189;
metastoma of, 189; pereiopod of,
188; pleopod of, 187; pleura of,
187; rostrum of, 185; sternum of,
186.

Lobster, swimmeret of, 186, 188; tel-
son of, 186 ; tergum of, 185, 187.

Macromere, 320.

388

INDEX.

Madrcporic body of Sea Urchin, 85 ; of
Starfish, 57, 69.

Malpighian tube, 262.

Mandible of Crab, 180; of CrabMega-
lops, 218; of Crab Zoea, 210, 211 ; of
Cyclops, 227 ; of Grasshopper, 211.

Mandibular palpus of Crab, 181, '211.

Maimbrium of Hydroid, 33; of Hydro
Medusa, 41.

Mantle of Anodouta, 274, 286, 287, 288;
of Squid, 334, 362 ; cavity of Anodon-
ta, 286, 288, 290, 291; cavity of Squid,
334, 337.

Maxilla of Crab, 176, 180, 196, 197 ; of
Crab Megalops, 218; of Crab Zoea,
210, 211; of Cyclops, 227 ; of Grass-
hopper, 246.

Maxillary palpus, 246.

Maxilliped of Crab, 175, 178, 196 ; of
Crab Megalops, 217, 219; of Crab
Zoea, 210 ; of Lobster, 189.

Medusa Buds of Hydroid, 50.

Medusa Ocellate, vii.

Medusa stage of Campanularian Hy-
droid, viii.

Megalops stage of Crab, 215.

Mentum, '21.">.

Meropodite, 176. •

Mesentery of Anodonta, 290.

Me-<nlenii of Sea Urchin, 108.

Mcsostcrnimi, '2 IS.

Metamorphosis of Crab, xxi ; of Cy-
clops, xxii; of Grasshopper, 256 ; of
Sea Krchin, xiv.

Meiasteruum, 248.

Metastoma of Crab, 180; of Cyclops,
226 ; of Grasshopper, 243 ; of Lob-
ster, 189.

Microraere, 321.

Micropyle, 364.

Mouth of Anodonta, 276, 284 ; of Crab ;
of Cyclops, 226; of Earthworm; of
Leech, 161, 167; of Sea Urchin, 129 ;
of Squid, 348, 355, 368; of Star-
fish, 57 ; of Hydroid ; of Hydro Me-
dusa ; papillae, 57.

Mucous Glands, 162.

Multiplication of Vorticella, 19.

Muscles of Anodonta, 272, 273, 274,
290 ; of Larva, 329, 331 ; of Crab, 192,
195; of Earthworm, 143, 152, 154,
156; of Sea Urchin, 97, 98; of Star-
fish, 68.

Muscles of Squid, 338, 355, 361.

Muscular layer of Medusa, 1"), 48.

Mytilus, gill of, 298; tentacles of, 300;
incurrent ostia of, 303 ; inter-lamel-
lar junctions of, 301 ; inter-tentacular
junctions of, 301.

Nauplius stage of Cyclops, 234.

Neck of Squid, 338.

Nematocyst,34.

Nervous system of Anodonta; of Crab,
205; of Earthworm, 116, 157; of
Grasshopper, 263 ; of Hydro Medusa,
46, 48 ; of Leech, 165, 166 ; of Sea
Urchin, 98; of Squid, 348, 353; of
Starfish, 70, 71.

Nidamental glands of Squid, 338, 352.

Nucleus, 320; of Amreba, 6; of Para-
mcecium, 12 ; of Vorticella, 19.

Nutritive pole of egg, 104.

Occipital foramen, 245.

Ocelli of Grasshopper, 243 ; of Leech ;
of Hydro Medusa, 42.

Occular plate of Sea Urchin, 85.

Ocellate Hydro Medusa, vii.

Odontophore, 356.

CEsophageal commissure of Crab, 205.

CEsophagus of Earthworm, 144, 159;
of Crab ; of Grasshopper, 261 ; of Sea
Urchin, 02, 94; of Squid, 346,357,
369 ; of Starfish, 68.

CEsophagus of Paramoecium, 10; of
Vorticella, 18.

CEsophageal glands of Earthworm, 144,
159.

Ophthalmic artery, 192, 195.

Orbital lobe, 170.

Orifice of invagination, 107.

Osculum, 23, 24.

Ossicle ambulacra!, 58, 61, 76, 88, 89.

Ossicle inter-ambulacral, 59, 75, 88, 89.

Ossicle, cardiac, 190.

INDEX.

389

Ossicle, pyloric, 192.

Otocyst of Hydro Medusa, ">•">.

Ovariolc, 263.

Ovary of Crab, 194, 204 ; of Cyclops,
229; of Earthworm, 152; of Ano-
donta ; of Grasshopper, 263 ; of Leech,
166 ; of Sea Urchin ; of Squid, 348,
353 ; of Starfish, 68.

Ovarian eggs, 312; plates, 85.

Oviduct of Crab, 204; of Grasshopper,
263; of Earthworm, 152 ; of Cyclops,
226, 228; of Leech, 166; of Squid,
353.

Ovipositor of Grasshopper, 251, 256.

Ovisac, 226.

Oyster development, xxviii.

Pallial line, 272.

Palpiger, 245.

Paramcecium, ii. ; anus of, 11 ; cilia of,
8; contractile vesicle of, 11; cuticle
of, 9; digestive organs, 10; ectosarc,
9; endoplast, 12 ; endosarc, 9; food
vacuole, 11; oesophagus, 10; peri-
stome, 10; sarcode, 9; vestibule, 10.

Parieto-splanchnic ganglia, 288.

Patagium, 250.

Pearly layer, 273.

Pedal ganglia of Anodonta, 246.

Pedicellarias 58, 73, 84.

Pen of Squid, 335, 363, 368.

Penis of Leech, 166.

Pereiopod, 175, 176, 188, 214, 217, 218.

Pericardium of Anodonta, 274, 281, 293 ;
of Crab, 192; of Squid, 343.

Pericardium of Starfish, 71.

Peri-ha-rnal vessels of Starlish, 71, 72,
77.

Periproct of Sea Urchin, 85.

Perisarc, 32.

IVri^oina, 57.

Peristomc of Crab, 179; of Paramce-
cium, 10 ; of Vorticella, 14 ; of Sea
Urchin, 84; of Starfish, 63, 68.

Perivisoeral Fluid, 143.

Pharynx of Earthworm, 143, 158; of
Leech, 163, 16 1.

Pleopod of Crab, 171; of Lobster, 187.

Pleura of Crab, 173; of Lobster, 187.

Pluteus of Sea Urchin, 110.

Podical plate, 253.

Polar globule, 319.

Polian vesicle, 69.

Postscutellum, 247.

Prescutum, 247.

Principal axis of egg, 103.

Prismatic layer, 273.

Proboscis, 160.

Pronotum, 246.

Propodite, 176.

Prostate gland, 350, 352.

Prosternum, 247.

Prothorax, 246.

Proventriculus, 261.

Protopoclite, 172, 175.

Pscudopodia, 4.

Pulvillus, 242.

Pupil of Squid, 358.

Pyloric coeca of Crab, 201 ; pouch of
( 'rah, 200 ; sac of Starfish, 64.

Racemose vesicle, 70.

llacliis, 57.

Radial water tube, 58, 69, 78, 91,96, 98.

Radula of Sea Urchin, 96 ; of Squid,
357.

Receptaculum scminis, 151.

Rectum of Anodonta, 274, 284, 286 ; of
Crab Zoea, '209 ; of Grasshopper, 262 ;
of Squid, 338, 346, 371.

Regeneration of lost parts, 36.

Renal organ of Anodonta, 281, 282;
of Lamellibranch embryo, 329; of
Squid, 340, 341.

Reproductive calycle, 49; organs of
Anodonta, 284, 296; of Crab, 204,
205 ; of Cyclops, 228. 230 ; of Earth-
worm, 149; of Grasshopper, 259,
263; of Hydro Medusa, 42; of
Leech, 161, 162, 166; of Sea Urchin,
91 ; of Squid, 349, 352 ; of Starfish,
68.

Respiratory organs of Crab, 195.

Respiratory tree, 65.

Keying Mau-o of egg, 104, 321.

Retina of Squid, 359.

390

INDEX.

Rostral septum, 183.

Rostrum of Crab, 169; of Crab Mega-
lops, 217; of Crab Zoea, 207; of Cy-
clops, 225 ; of Lobster, 185.

Salivary glands, 261, 347.

Sarcode, 4, 9.

Scaphognuthite, 178, 180, 212.

Scutellum, 247.

Scutum, 247.

Sea Urchin, xii, xiii, xiv.; ab-actinal
surface, 83; actinal surface, 83,
89; alveoli, 95; ambulacra, 84;
ambulacral area, 88; ambulacral
pore, 88; ambulacral suture, 88;
ambulacral vesicle, 91, 98; anal
plate, 85; auriculae, 90, 98; corona,
fa">; development of, 126; eggs, 90,
102 ; epiphysis, 96 ; gastrula stage,
107; hard parts, xii ; heart, 94; inter-
ambulacral area, 88 ; inter-radial su-
ture, 87 ; internal structure, xiii ; in-
testine, 92, 94 ; madreporic body, 85 ;
mouth, 88, 129 ; muscles, 97, 98 ;
nervous system, 94, 98 ; occular plate,
85 ; oesophagus, 92, 94; ovarian plate,
85 ; pedicellariae, 84 ; peristome, 84 ;
periproct, 85 ; pluteus, 110 ; radii, 96 ;
radulae, 96 ; reproductive organs, 91 ;
segmentation, 102 ; spermatozoa, 100 ;
spines, 84 ; stone-canal, 93 ; teeth, 84,
90, 97 ; water tube, 91, 93, 98.

Segmental organ, 162.

Segmentation, 102, 319, 365; nuclei,
105; cavity, 107.

Segmentation partial regular, 364 ; par-
tial irregular, 364 ; total, 364.

Seminal fluid, 313; receptacle, 151,
204 ; vesicle, 149.

Setae, 157, 226, 332.

Setigerous glands, 152.

Shell, 271, 335, 368; gland, 226, 368.

Sinus, 195 ; venosus, 294.

Siphon, 272, 336, 338, 339, 361, 368, 370,
377.

Somite, 182.

Spermatheca of Cyclops, 229 ; of Grass-
hopper, 263.

Spermatic duct, 229.

Spcrmatophore, 232, 352 ; sac, 232.

Spermatozoa, 100, 233, 314, 332.

Spiciilcs, 25, 112.

Spines, 84.

Spiracle, 249, 251.

Spleen of Squid, 345, 316.

Sponge, v. ; budding in, 25; cloaca, 23,
24; endoderm, 29; osculum, 23,24;
spicules, 25; syncitium, 29.

Squid, x\ix., xxx. : arrtahula of, 337 ;
anus of, 339; anal valve of, 378;
aorta anterior of, 345, 347 ; aorta
posterior of, 345 ; arms of, 333, 336,
337, 369; auditory nerve of, 363;
auditory organ of, 363, 372 ; beak of,
333, 348, 1555 ; blastoderm of, 365 ;
branchial artery of, 340, 343 ; bran-
chial heart of, 343, 343, 372 ; bran-
chial vein of, 340, 345 ; buccal body of,
348, 354 ; chromatophorc of, 334, 373,
379; ciliary body of, 359; commis-
sure, brachial of, 354 ; cerebro-
brachial of, 356, 357 ; circulatory
organs of, 341 ; cornea of, 358 ; cra-
nium of, 348; development of,
xxx.; digestive organs of, 345; ear
of, 372 ; ear capsule of, 363 ; ear de-
velopment of, 368 ; egg of, 364 ; eye
of, 357 ; eye, anterior chamber of,
358 ; eye, development of, 368 ; eye,
invagination of, 367 ; eye, posterior
chamber of, 358 ; eye-stalk of, 367,
370 ; ganglion, brachial of, 354 ;
ganglion, cerebral of, 360 ; ganglion,
ciliary of, 359; ganglion, optic of,
360, 371; ganglion, pedal of, 357,
360; ganglion of retina of, 366; gan-
glion, stflhituni of, 338 ; ganglion,
visceral of, 363 ; germinal area of,
365 ; gill of, 340, 343, 373 ; gill, de-
velopment of, 368; head of, 333;
head, cartilage of, 361, 363 ; hecto-
cotylus of, 349 ; hepatic duct of, 348;
ink bag of, 339, 378 ; intestine of, 339,
346 ; iris of, 358 ; jaws of, 348 ; lens
of, 358, 359 ; lingual ribbon of, 348,

INDEX.

391

357 ; liver of, 344, 347 ; mantle of,
334, 362, 378 ; mantle artery of, 340,
343; mantle cartilage of, 338; mau-
tle chamber of, 334, 337 ; mantle cir-
culation of, 376 ; mantle develop-
ment of, 367 ; micropyle of, 364 ;
moutli of, 348, 355; mouth develop-
ment of, 368; muscles of, 338,355,
361; neck of, 338; nervous system
of, 3 18,353; nidamcntal gland of, 338,
352 ; odontophore of, 356 ; oesophagus,
346, 347, 348, 357 ; oesophagus devel-
opment of, 369 ; olfactory organ of,
333 ; otocyst of, 372 ; ovary of, 348,
353; oviduct of, 353; pen of, 335,
363, 368 ; pericardium of, 343 ; pros-
tate gland of, 350, 352; pupil of, 358 ;
rachis of, 357 ; radula of, 357 ; rec-
tum of, 338, 346, 371; regions of
body of, • !3 I ; renal organ of, 340, 341 ;
reproductive organs of, male, 349;
reproductive organs of, female, 352 ;
retina of, 359; salivary gland of, 347,
segmentation of, 365 ; shell of, 335,
363, 368; shell gland of, 368; siphon
of, 336, 338,339, 361, 370; siphon de-
velopment of, 3G8 ; siphon valve of,
336,377; siphonal cartilage of, 338;
spermatophore of, 352 ; spermato-
phore receptacle of, 350, 351 ; sperma-
tozoa of, 352 ; spleen of, 345, 346 ;
stomach of, 316; systemic heart of,
345; test is of, 348,349; vas deferens
of, 350 ; vas effercns of, 351 ; vena
cava anterior of, 341, 314, 362 ; vena
cava posterior of, 310,343; vesicula
seminalcs of, 350; visceral sac of,
341 ; vitreous humor, 35! >.
Starfish, ix. , x., xi. ; ab-actinal snrlMcv of,
57 ; ab-oral tentacle of, G3, 75 ; m'tinal
surface of, 57 ; ambulacra of, 63, 69,
76; ambulacra! area of, 60, 61; am-
bulacral furrow of, 57; ambulacra!
pore of, 57; ambulacra! system of,
68, 69, 76; ambulacra! vesicle of, 69;
ampullae of, 69 ; anterior ray of, 57 ;
bivium of, 58; blood-vessels of, 71,

77 ; digestive organs of, 63 ; heart of,
71 ; hepatic coeca of, 63, 64, 75 ; inter-
ambulacral area of, 61 ; inter-radius
of, 57, 65 ; inter-radial partition of,
62 ; intestine of, 65 ; madreporic
body of, 57, 69 ; microscopic struct-
ure of, xi.; mouth of, 57; nervous
system of, 70, 71 ; oesophagus of, 68;
ossicle of, 58, 59, 61, 75, 76; pedicel-
lariue of, 58, 73 ; pericardium of, 71 ;
perihamial vessel of, 71, 72, 76; peri-
soma of, 57 ; peristome of, 63, 68 ;
polian vesicle of, 69 ; pyloric sac of,
64; racemose vesicle of, 70; repro-
ductive organs of, 68 ; respiratory
tree of, 65 ; stomach of, 63, 65, 67,
75 ; stomach muscles of, 68 ; stone
canal of, 71 ; swimming larva of,
130; tiivium of, 58; vertebral ridge
of, 60 ; water system of, 68, 69, 76.

Sternal artery, 195 ; plastron, 174, 183,
171.

Sternum, 173, 184.

Stipes, 210.

Stomach of Anodonta, 284, 296; of
Crab, 190, 200; of Zoea, 209; of
Starfish, 63, 65, 67, 68 ; of Hydro
Medusa, 41 ; of Leech, 163, 164 ; of
Squid, 346.

Stomato-gastric ganglia, 167.

Stone canal, 71, 93.

Sub-genital plate, 251.

Submentum, 245.

Sub-oesophageal ganglia, 264.

Sub-umbrella, 39.

Supporting layer, 33, 45, 48.

Supra-cesophageal ganglia, 263.

Surface collecting, 37.

Swimmeret, 186, 188.

Syncitium, 29.

Systemic heart of Squid, 345.

Tarsus, 242.

Teeth, 84, 85, 97.

Tegmina, 238.

Telsou, 186, 207, 214, 217.

Tentacles ab-oral, 63, 75 ; of Hydro
Medusa, 40, 45-

392

INDEX.

Tergum, 171, 173, 185, 187.

Testis of Crab, 205 ; of Cyclops, 230 ;
of Earthworm, 144, 149; of Leech,
166 ; of Squid, 348, 349.

Thoracic area, 170.

Thoracic ganglia, 206; of Crab, of
Grasshopper, 264.

Thorax of Cyclops, 225 ; of Grasshop-
per, 238, 246.

Tibia, 242.

Tongue, 245.

Trachea, 259.

Trivium, 58.

Trochanter, 240.

Tubular band, 158.

Tympanum, 264.

Umbrella, 39.

Ungues, 242.

Unio, gill of, 305.

Vagina, 166, 263.

Vas deferens of Crab, 177, 205 ; of Cy-
clops, 230; of Earthworm, 150; of
Squid, 350.

Veliger, embryo, 327.

Velum of Hydro Medusa, 39; of Oys-
ter, 329 ; of Squid, 369.

Venous sinus, 282.

Ventral nerve chain of Earthworm,
148, 157 ; of Grasshopper, 263 ; of
Leech, 165.

Ventricle of Auodonta, 281, 282, 293.

Ventriculus, 262.

Vertebral ridge, 60.

Vesicula seminales, 149, 166, 350,

Vestibule, 10, 15, 18.

Vitreous humor, 359.

Vorticella, iii. : conjugation of, 21 :
contractile vesicle of, 19; crop of, 18;
cuticle of, 17 ; digestive organs of,
ectosarc of, 17 ; encystment of, 22 ;
endoplast of, 19 ; endosarc of, 16 ;
epistorna of, 15 ; fission of, 20 ; food
vacuole of, 19; oesophagus of, 18;
peristome of, 14 ; vestibule of, 15, 18.

Water pouch of Echinoderms, 109 ;
system, 68, 69, 76; tube, radial,
58, 69, 70, 78, 91, 98 ; tube, circum-
oral, 70, 93 ; unio, 306.

Wings, 238, 239.

Wing cover, 238.

Zoea stage of Crab, 207 ; embry-
onic, 214.

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